Trial Outcomes & Findings for PF-06804103 Dose Escalation in HER2 Positive and Negative (Negative Only in Part 2) Solid Tumors (NCT NCT03284723)

Last Updated: 2024-09-03

Results Overview

A DLT was any of the following adverse events(AEs) in the first cycle of treatment (within 21 days of first dose). (1) Hematologic: Grade 4 neutropenia lasting \>7 days; febrile neutropenia; Grade \>＝3 neutropenic infection; Grade \>＝3 thrombocytopenia with bleeding; thrombocytopenia; (2) Non-hematologic: Grade \>=3 toxicities that were considered clinically significant; delayed by more than 2 weeks in receiving the next scheduled cycle due to persisting treatment related toxicities; concurrent AST or ALT \>3x ULN and total bilirubin \>2x ULN; any Grade 5 event.

Recruitment status

TERMINATED

Study phase

PHASE1

Target enrollment

95 participants

Primary outcome timeframe

First cycle, Day 1 up to Day 21

Results posted on

2024-09-03

Participant Flow

Part A (PF-06804103 monotherapy) included Part 1A (dose escalation part) and Part 2A (dose expansion part). Part B (PF-06804103 plus palbociclib and letrozole combination therapy) included Part 1B (dose escalation part).

In Part 1A, 47 participants were treated at dose levels of PF-06804103 0.15, 0.5, 1.2, 2.0, 3.0, 4.0 and 5.0 mg/kg. In Part 2A, 46 participants were treated at dose levels of PF-06804103 3.0 and 4.0 mg/kg. In Part 1B, 2 participants received PF-06804103 2.0 mg/kg in combination with standard of care (SOC) doses of palbociclib and letrozole. Participants were unique in each part.

Participant milestones

Participant milestones
Measure	PART 1A PF-06804103 0.15 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.15 mg/kg on Day 1 of each 21-day cycle as an intravenous (IV) infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks. HER2 = Human Epidermal Growth Factor Receptor 2; BC = breast cancer; GC = gastric and gastroesophageal cancer.	PART 1A PF-06804103 0.5 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.5 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 1.2 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 1.2 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 2.0 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 2.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 3.0 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 4.0 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 5.0 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 5.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 2A PF-06804103 3.0 mg/kg HER2+ BC Participants with HER2-positive BC in third line (3L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 4.0 mg/kg HER2+ BC Participants with HER2-positive BC in 3L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 3.0 mg/kg HR+ HER2-Low BC Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in second line (2L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks. HR = hormone receptor; IHC = immunohistochemistry; ISH = in-situ hybridization.	PART 2A PF-06804103 4.0 mg/kg HR+ HER2-Low BC Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in 2L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 1B PF-06804103 2.0 mg/kg HR+ HER2-Low Combo BC Postmenopausal participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC received PF-06804103 at 2.0 mg/kg once every 14 days in a 28-day cycle as an IV infusion. The maximum duration of treatment for Part 1B was approximately 53.7 weeks.
Overall Study STARTED	2	2	2	4	16	15	6	5	14	12	15	2
Overall Study Received Treatment	2	2	2	4	16	15	6	5	14	12	15	2
Overall Study COMPLETED	1	2	1	3	9	10	3	5	6	7	9	0
Overall Study NOT COMPLETED	1	0	1	1	7	5	3	0	8	5	6	2

Reasons for withdrawal

Reasons for withdrawal
Measure	PART 1A PF-06804103 0.15 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.15 mg/kg on Day 1 of each 21-day cycle as an intravenous (IV) infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks. HER2 = Human Epidermal Growth Factor Receptor 2; BC = breast cancer; GC = gastric and gastroesophageal cancer.	PART 1A PF-06804103 1.2 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 1.2 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 2.0 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 2.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 3.0 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 4.0 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 5.0 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 5.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 2A PF-06804103 4.0 mg/kg HER2+ BC Participants with HER2-positive BC in 3L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 3.0 mg/kg HR+ HER2-Low BC Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in second line (2L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks. HR = hormone receptor; IHC = immunohistochemistry; ISH = in-situ hybridization.	PART 2A PF-06804103 4.0 mg/kg HR+ HER2-Low BC Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in 2L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 1B PF-06804103 2.0 mg/kg HR+ HER2-Low Combo BC Postmenopausal participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC received PF-06804103 at 2.0 mg/kg once every 14 days in a 28-day cycle as an IV infusion. The maximum duration of treatment for Part 1B was approximately 53.7 weeks.
Overall Study Death	0	0	1	0	0	1	0	2	1	0
Overall Study Lost to Follow-up	0	0	0	0	2	1	0	2	0	0
Overall Study Study Terminated By Sponsor	0	0	0	1	0	0	1	1	1	1
Overall Study Withdrawal by Subject	0	0	0	5	3	1	6	0	3	1
Overall Study Other	1	1	0	1	0	0	0	0	1	0
Overall Study Adverse Event	0	0	0	0	0	0	1	0	0	0

Baseline Characteristics

PF-06804103 Dose Escalation in HER2 Positive and Negative (Negative Only in Part 2) Solid Tumors

Baseline characteristics by cohort

Baseline characteristics by cohort
Measure	PART 1A PF-06804103 0.15 mg/kg n=2 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.15 mg/kg on Day 1 of each 21-day cycle as an intravenous (IV) infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks. HER2 = Human Epidermal Growth Factor Receptor 2; BC = breast cancer; GC = gastric and gastroesophageal cancer.	PART 1A PF-06804103 0.5 mg/kg n=2 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.5 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 1.2 mg/kg n=2 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 1.2 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 2.0 mg/kg n=4 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 2.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 3.0 mg/kg n=16 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 4.0 mg/kg n=15 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 5.0 mg/kg n=6 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 5.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 2A PF-06804103 3.0 mg/kg HER2+ BC n=5 Participants Participants with HER2-positive BC in third line (3L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 4.0 mg/kg HER2+ BC n=14 Participants Participants with HER2-positive BC in 3L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 3.0 mg/kg HR+ HER2-Low BC n=12 Participants Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in second line (2L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks. HR = hormone receptor; IHC = immunohistochemistry; ISH = in-situ hybridization.	PART 2A PF-06804103 4.0 mg/kg HR+ HER2-Low BC n=15 Participants Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in 2L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 1B PF-06804103 2.0 mg/kg HR+ HER2-Low Combo BC n=2 Participants Postmenopausal participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC received PF-06804103 at 2.0 mg/kg once every 14 days in a 28-day cycle as an IV infusion. The maximum duration of treatment for Part 1B was approximately 53.7 weeks.	Total n=95 Participants Total of all reporting groups
Age, Continuous	49.0 Years STANDARD_DEVIATION 19.8 • n=5 Participants	65.5 Years STANDARD_DEVIATION 0.71 • n=7 Participants	58.0 Years STANDARD_DEVIATION 11.31 • n=5 Participants	67.0 Years STANDARD_DEVIATION 4.69 • n=4 Participants	54.5 Years STANDARD_DEVIATION 11.06 • n=21 Participants	53.1 Years STANDARD_DEVIATION 11.70 • n=10 Participants	55.5 Years STANDARD_DEVIATION 11.33 • n=115 Participants	50.8 Years STANDARD_DEVIATION 6.57 • n=24 Participants	50.0 Years STANDARD_DEVIATION 8.68 • n=42 Participants	58.3 Years STANDARD_DEVIATION 10.36 • n=42 Participants	53.8 Years STANDARD_DEVIATION 11.67 • n=42 Participants	53.0 Years STANDARD_DEVIATION 9.90 • n=42 Participants	54.5 Years STANDARD_DEVIATION 10.74 • n=36 Participants
Age, Customized <18	0 Participants n=5 Participants	0 Participants n=7 Participants	0 Participants n=5 Participants	0 Participants n=4 Participants	0 Participants n=21 Participants	0 Participants n=10 Participants	0 Participants n=115 Participants	0 Participants n=24 Participants	0 Participants n=42 Participants	0 Participants n=42 Participants	0 Participants n=42 Participants	0 Participants n=42 Participants	0 Participants n=36 Participants
Age, Customized 18-44	1 Participants n=5 Participants	0 Participants n=7 Participants	0 Participants n=5 Participants	0 Participants n=4 Participants	3 Participants n=21 Participants	4 Participants n=10 Participants	1 Participants n=115 Participants	1 Participants n=24 Participants	5 Participants n=42 Participants	1 Participants n=42 Participants	5 Participants n=42 Participants	0 Participants n=42 Participants	21 Participants n=36 Participants
Age, Customized 45-64	1 Participants n=5 Participants	0 Participants n=7 Participants	1 Participants n=5 Participants	1 Participants n=4 Participants	10 Participants n=21 Participants	8 Participants n=10 Participants	4 Participants n=115 Participants	4 Participants n=24 Participants	8 Participants n=42 Participants	7 Participants n=42 Participants	7 Participants n=42 Participants	2 Participants n=42 Participants	53 Participants n=36 Participants
Age, Customized >=65	0 Participants n=5 Participants	2 Participants n=7 Participants	1 Participants n=5 Participants	3 Participants n=4 Participants	3 Participants n=21 Participants	3 Participants n=10 Participants	1 Participants n=115 Participants	0 Participants n=24 Participants	1 Participants n=42 Participants	4 Participants n=42 Participants	3 Participants n=42 Participants	0 Participants n=42 Participants	21 Participants n=36 Participants
Sex: Female, Male Female	0 Participants n=5 Participants	1 Participants n=7 Participants	1 Participants n=5 Participants	2 Participants n=4 Participants	11 Participants n=21 Participants	10 Participants n=10 Participants	4 Participants n=115 Participants	5 Participants n=24 Participants	14 Participants n=42 Participants	12 Participants n=42 Participants	15 Participants n=42 Participants	2 Participants n=42 Participants	77 Participants n=36 Participants
Sex: Female, Male Male	2 Participants n=5 Participants	1 Participants n=7 Participants	1 Participants n=5 Participants	2 Participants n=4 Participants	5 Participants n=21 Participants	5 Participants n=10 Participants	2 Participants n=115 Participants	0 Participants n=24 Participants	0 Participants n=42 Participants	0 Participants n=42 Participants	0 Participants n=42 Participants	0 Participants n=42 Participants	18 Participants n=36 Participants
Ethnicity (NIH/OMB) Hispanic or Latino	0 Participants n=5 Participants	1 Participants n=7 Participants	0 Participants n=5 Participants	0 Participants n=4 Participants	2 Participants n=21 Participants	1 Participants n=10 Participants	0 Participants n=115 Participants	0 Participants n=24 Participants	0 Participants n=42 Participants	1 Participants n=42 Participants	1 Participants n=42 Participants	0 Participants n=42 Participants	6 Participants n=36 Participants
Ethnicity (NIH/OMB) Not Hispanic or Latino	2 Participants n=5 Participants	1 Participants n=7 Participants	2 Participants n=5 Participants	4 Participants n=4 Participants	14 Participants n=21 Participants	14 Participants n=10 Participants	6 Participants n=115 Participants	5 Participants n=24 Participants	14 Participants n=42 Participants	11 Participants n=42 Participants	13 Participants n=42 Participants	2 Participants n=42 Participants	88 Participants n=36 Participants
Ethnicity (NIH/OMB) Unknown or Not Reported	0 Participants n=5 Participants	0 Participants n=7 Participants	0 Participants n=5 Participants	0 Participants n=4 Participants	0 Participants n=21 Participants	0 Participants n=10 Participants	0 Participants n=115 Participants	0 Participants n=24 Participants	0 Participants n=42 Participants	0 Participants n=42 Participants	1 Participants n=42 Participants	0 Participants n=42 Participants	1 Participants n=36 Participants
Race (NIH/OMB) American Indian or Alaska Native	0 Participants n=5 Participants	0 Participants n=7 Participants	0 Participants n=5 Participants	0 Participants n=4 Participants	0 Participants n=21 Participants	0 Participants n=10 Participants	0 Participants n=115 Participants	0 Participants n=24 Participants	0 Participants n=42 Participants	0 Participants n=42 Participants	0 Participants n=42 Participants	0 Participants n=42 Participants	0 Participants n=36 Participants
Race (NIH/OMB) Asian	0 Participants n=5 Participants	0 Participants n=7 Participants	0 Participants n=5 Participants	2 Participants n=4 Participants	4 Participants n=21 Participants	5 Participants n=10 Participants	1 Participants n=115 Participants	1 Participants n=24 Participants	9 Participants n=42 Participants	1 Participants n=42 Participants	3 Participants n=42 Participants	2 Participants n=42 Participants	28 Participants n=36 Participants
Race (NIH/OMB) Native Hawaiian or Other Pacific Islander	0 Participants n=5 Participants	0 Participants n=7 Participants	0 Participants n=5 Participants	0 Participants n=4 Participants	0 Participants n=21 Participants	0 Participants n=10 Participants	0 Participants n=115 Participants	0 Participants n=24 Participants	0 Participants n=42 Participants	0 Participants n=42 Participants	0 Participants n=42 Participants	0 Participants n=42 Participants	0 Participants n=36 Participants
Race (NIH/OMB) Black or African American	1 Participants n=5 Participants	0 Participants n=7 Participants	0 Participants n=5 Participants	0 Participants n=4 Participants	0 Participants n=21 Participants	0 Participants n=10 Participants	0 Participants n=115 Participants	0 Participants n=24 Participants	1 Participants n=42 Participants	0 Participants n=42 Participants	0 Participants n=42 Participants	0 Participants n=42 Participants	2 Participants n=36 Participants
Race (NIH/OMB) White	1 Participants n=5 Participants	1 Participants n=7 Participants	2 Participants n=5 Participants	2 Participants n=4 Participants	10 Participants n=21 Participants	10 Participants n=10 Participants	5 Participants n=115 Participants	4 Participants n=24 Participants	4 Participants n=42 Participants	11 Participants n=42 Participants	12 Participants n=42 Participants	0 Participants n=42 Participants	62 Participants n=36 Participants
Race (NIH/OMB) More than one race	0 Participants n=5 Participants	0 Participants n=7 Participants	0 Participants n=5 Participants	0 Participants n=4 Participants	2 Participants n=21 Participants	0 Participants n=10 Participants	0 Participants n=115 Participants	0 Participants n=24 Participants	0 Participants n=42 Participants	0 Participants n=42 Participants	0 Participants n=42 Participants	0 Participants n=42 Participants	2 Participants n=36 Participants
Race (NIH/OMB) Unknown or Not Reported	0 Participants n=5 Participants	1 Participants n=7 Participants	0 Participants n=5 Participants	0 Participants n=4 Participants	0 Participants n=21 Participants	0 Participants n=10 Participants	0 Participants n=115 Participants	0 Participants n=24 Participants	0 Participants n=42 Participants	0 Participants n=42 Participants	0 Participants n=42 Participants	0 Participants n=42 Participants	1 Participants n=36 Participants

PRIMARY outcome

Timeframe: First cycle, Day 1 up to Day 21

Population: Participants enrolled in Part 1A who received at least 1 dose of study treatment and who did not have major treatment deviations during first cycle.

Outcome measures

Outcome measures
Measure	PART 1A PF-06804103 0.15 mg/kg n=2 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.15 mg/kg on Day 1 of each 21-day cycle as an intravenous (IV) infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks. HER2 = Human Epidermal Growth Factor Receptor 2; BC = breast cancer; GC = gastric and gastroesophageal cancer.	PART 1A PF-06804103 0.5 mg/kg n=2 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.5 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 1.2 mg/kg n=2 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 1.2 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 2.0 mg/kg n=4 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 2.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 3.0 mg/kg n=16 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 4.0 mg/kg n=15 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 5.0 mg/kg n=6 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 5.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 2A PF-06804103 3.0 mg/kg HER2+ BC Participants with HER2-positive BC in third line (3L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 4.0 mg/kg HER2+ BC Participants with HER2-positive BC in 3L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 3.0 mg/kg HR+ HER2-Low BC Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in second line (2L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks. HR = hormone receptor; IHC = immunohistochemistry; ISH = in-situ hybridization.	PART 2A PF-06804103 4.0 mg/kg HR+ HER2-Low BC Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in 2L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 1B PF-06804103 2.0 mg/kg HR+ HER2-Low Combo BC Postmenopausal participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC received PF-06804103 at 2.0 mg/kg once every 14 days in a 28-day cycle as an IV infusion. The maximum duration of treatment for Part 1B was approximately 53.7 weeks.
Number of Participants With Cycle 1 (21 Days) Dose-Limiting Toxicities (DLTs) in Part 1A	0 Participants	0 Participants	0 Participants	0 Participants	2 Participants	2 Participants	0 Participants	—	—	—	—	—

PRIMARY outcome

Timeframe: First Cycle, Day 1 up to Day 28

Population: Participants enrolled in Part 1B who received at least 1 dose of study treatment and who did not have major treatment deviations during first cycle.

A DLT was any of the following adverse events(AEs) in the first cycle of treatment (within 28 days of first dose). (1) Hematologic: including a delay greater than 1 week in administration of the next scheduled dose of study treatment due to persistent treatment-related toxicities; Grade 4 neutropenia lasting \>7 days; febrile neutropenia; Grade \>=3 neutropenic infection; Grade \>=3 thrombocytopenia with bleeding; thrombocytopenia. (2) Non-hematologic: including Grade \>=3 toxicities that are considered clinically significant; Grade 3 QTc prolongation despite correction of reversible causes; delayed by \>2 week in receiving the next scheduled dose of any study treatment due to persisting treatment-related toxicities; inability to administer at least 80% of the planned palbociclib or letrozole or 100% of the planned PF-06804103 doses during Cycle 1 due to toxicity related to the study treatment; concurrent AST or ALT \>3x ULN and total bilirubin \>2x ULN; any Grade 5 event.

Outcome measures

Outcome measures
Measure	PART 1A PF-06804103 0.15 mg/kg n=1 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.15 mg/kg on Day 1 of each 21-day cycle as an intravenous (IV) infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks. HER2 = Human Epidermal Growth Factor Receptor 2; BC = breast cancer; GC = gastric and gastroesophageal cancer.	PART 1A PF-06804103 0.5 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.5 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 1.2 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 1.2 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 2.0 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 2.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 3.0 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 4.0 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 5.0 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 5.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 2A PF-06804103 3.0 mg/kg HER2+ BC Participants with HER2-positive BC in third line (3L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 4.0 mg/kg HER2+ BC Participants with HER2-positive BC in 3L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 3.0 mg/kg HR+ HER2-Low BC Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in second line (2L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks. HR = hormone receptor; IHC = immunohistochemistry; ISH = in-situ hybridization.	PART 2A PF-06804103 4.0 mg/kg HR+ HER2-Low BC Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in 2L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 1B PF-06804103 2.0 mg/kg HR+ HER2-Low Combo BC Postmenopausal participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC received PF-06804103 at 2.0 mg/kg once every 14 days in a 28-day cycle as an IV infusion. The maximum duration of treatment for Part 1B was approximately 53.7 weeks.
Number of Participants Wth Cycle 1 (28 Days) Dose-Limiting Toxicities (DLTs) in Part 1B	0 Participants	—	—	—	—	—	—	—	—	—	—	—

PRIMARY outcome

Timeframe: From the first dose of study treatment up to a minimum of 28 calendar days after the last dose of study treatment (maximum duration between first and last dose: 89.3 weeks for Part 1A, 49.4 weeks for Part 2A, 53.7 weeks for Part 1B)

Population: All enrolled participants who received at least one dose of study treatment.

An AE was any untoward medical occurrence in a participant who received study drug without regard to possibility of causal relationship. A serious adverse event (SAE) was an AE resulting in any of the following outcomes or deemed significant for any other reason: death; initial or prolonged inpatient hospitalization; life-threatening experience (immediate risk of dying); persistent or significant disability/incapacity; congenital anomaly. Treatment-emergent AEs (TEAEs) were defined as those with initial onset or increasing in severity after the first dose of study medication. A treatment-related AE was any untoward medical occurrence attributed to the study drug in a participant who received study drug. Relatedness to study drug was assessed by the investigator.

Outcome measures

Outcome measures
Measure	PART 1A PF-06804103 0.15 mg/kg n=2 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.15 mg/kg on Day 1 of each 21-day cycle as an intravenous (IV) infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks. HER2 = Human Epidermal Growth Factor Receptor 2; BC = breast cancer; GC = gastric and gastroesophageal cancer.	PART 1A PF-06804103 0.5 mg/kg n=2 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.5 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 1.2 mg/kg n=2 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 1.2 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 2.0 mg/kg n=4 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 2.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 3.0 mg/kg n=16 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 4.0 mg/kg n=15 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 5.0 mg/kg n=6 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 5.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 2A PF-06804103 3.0 mg/kg HER2+ BC n=5 Participants Participants with HER2-positive BC in third line (3L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 4.0 mg/kg HER2+ BC n=14 Participants Participants with HER2-positive BC in 3L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 3.0 mg/kg HR+ HER2-Low BC n=12 Participants Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in second line (2L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks. HR = hormone receptor; IHC = immunohistochemistry; ISH = in-situ hybridization.	PART 2A PF-06804103 4.0 mg/kg HR+ HER2-Low BC n=15 Participants Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in 2L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 1B PF-06804103 2.0 mg/kg HR+ HER2-Low Combo BC n=2 Participants Postmenopausal participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC received PF-06804103 at 2.0 mg/kg once every 14 days in a 28-day cycle as an IV infusion. The maximum duration of treatment for Part 1B was approximately 53.7 weeks.
Number of Participants With All-Causality Treatment Emergent Adverse Events (TEAEs) and Serious Adverse Event (SAEs), Treatment-Related TEAEs and SAEs Number of Participants with all-causality TEAEs	2 Participants	2 Participants	2 Participants	4 Participants	16 Participants	15 Participants	6 Participants	5 Participants	14 Participants	12 Participants	15 Participants	2 Participants
Number of Participants With All-Causality Treatment Emergent Adverse Events (TEAEs) and Serious Adverse Event (SAEs), Treatment-Related TEAEs and SAEs Number of Participants with all-causality SAEs	1 Participants	0 Participants	0 Participants	1 Participants	7 Participants	5 Participants	4 Participants	2 Participants	6 Participants	5 Participants	7 Participants	0 Participants
Number of Participants With All-Causality Treatment Emergent Adverse Events (TEAEs) and Serious Adverse Event (SAEs), Treatment-Related TEAEs and SAEs Number of Participants with treatment-related TEAEs	1 Participants	1 Participants	1 Participants	4 Participants	15 Participants	15 Participants	6 Participants	5 Participants	14 Participants	10 Participants	15 Participants	2 Participants
Number of Participants With All-Causality Treatment Emergent Adverse Events (TEAEs) and Serious Adverse Event (SAEs), Treatment-Related TEAEs and SAEs Number of Participants with treatment-related SAEs	0 Participants	0 Participants	0 Participants	0 Participants	3 Participants	1 Participants	2 Participants	2 Participants	5 Participants	1 Participants	5 Participants	0 Participants

PRIMARY outcome

Timeframe: From baseline to end of treatment (maximum treatment duration: 89.3 weeks for Part 1A, 49.4 weeks for Part 2A, 53.7 weeks for Part 1B)

Population: Participants who had at least one on-treatment assessment for the corresponding lab parameter.

Participants who experienced hematology laboratory test abnormalities were summarized according to worst toxicity grade observed for each hematology laboratory test. Laboratory abnormalities were graded by NCI CTCAE version 4.03 (Grade 0: no change from normal or reference range; Grade 1: mild AE; Grade 2: moderate AE; Grade 3: severe AE; Grade 4: life-threatening consequences, urgent intervention indicated). This outcome measure calculated the number of participants with hematology laboratory abnormalities that were shifted from \<=Grade 2 at baseline to Grade 3 or above, including the following parameters: anemia, INR increased, lymphocyte count decreased, neutrophil count decreased, white blood cell decreased.

Outcome measures

Outcome measures
Measure	PART 1A PF-06804103 0.15 mg/kg n=2 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.15 mg/kg on Day 1 of each 21-day cycle as an intravenous (IV) infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks. HER2 = Human Epidermal Growth Factor Receptor 2; BC = breast cancer; GC = gastric and gastroesophageal cancer.	PART 1A PF-06804103 0.5 mg/kg n=2 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.5 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 1.2 mg/kg n=2 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 1.2 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 2.0 mg/kg n=4 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 2.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 3.0 mg/kg n=16 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 4.0 mg/kg n=15 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 5.0 mg/kg n=6 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 5.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 2A PF-06804103 3.0 mg/kg HER2+ BC n=5 Participants Participants with HER2-positive BC in third line (3L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 4.0 mg/kg HER2+ BC n=14 Participants Participants with HER2-positive BC in 3L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 3.0 mg/kg HR+ HER2-Low BC n=12 Participants Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in second line (2L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks. HR = hormone receptor; IHC = immunohistochemistry; ISH = in-situ hybridization.	PART 2A PF-06804103 4.0 mg/kg HR+ HER2-Low BC n=15 Participants Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in 2L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 1B PF-06804103 2.0 mg/kg HR+ HER2-Low Combo BC n=2 Participants Postmenopausal participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC received PF-06804103 at 2.0 mg/kg once every 14 days in a 28-day cycle as an IV infusion. The maximum duration of treatment for Part 1B was approximately 53.7 weeks.
Number of Participants With Laboratory Abnormalities-Hematology Anemia	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	1 Participants	1 Participants	0 Participants	0 Participants
Number of Participants With Laboratory Abnormalities-Hematology INR increased	0 Participants	0 Participants	1 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	1 Participants	0 Participants	0 Participants
Number of Participants With Laboratory Abnormalities-Hematology Lymphocyte count decreased	0 Participants	0 Participants	1 Participants	2 Participants	2 Participants	1 Participants	0 Participants	0 Participants	2 Participants	2 Participants	0 Participants	0 Participants
Number of Participants With Laboratory Abnormalities-Hematology Neutrophil count decreased	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	1 Participants	0 Participants	3 Participants	0 Participants	0 Participants	0 Participants
Number of Participants With Laboratory Abnormalities-Hematology White blood cell decreased	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	1 Participants	0 Participants	3 Participants	0 Participants	0 Participants	1 Participants

PRIMARY outcome

Timeframe: From baseline to end of treatment (maximum treatment duration: 89.3 weeks for Part 1A, 49.4 weeks for Part 2A, 53.7 weeks for Part 1B)

Population: Participants who had at least one on-treatment assessment for the corresponding lab parameter.

Participants who experienced chemistry laboratory test abnormalities were summarized according to worst toxicity grade observed for each chemistry laboratory test. Laboratory abnormalities were graded by NCI CTCAE version 4.03 (Grade 0: no change from normal or reference range; Grade 1: mild AE; Grade 2: moderate AE; Grade 3: severe AE; Grade 4: life-threatening consequences, urgent intervention indicated). This outcome measure calculated the number of participants with chemistry laboratory abnormalities that were shifted from \<=Grade 2 at baseline to Grade 3 or above, including the following parameters: alanine aminotransferase (ALT) increased, alkaline phosphatase (ALP) increased, aspartate aminotransferase (AST) increased, hyperglycemia, hypermagnesemia, hypocalcemia, hypokalemia, hyponatremia, hypophosphatemia, lipase increased, serum amylase increased.

Outcome measures

Outcome measures
Measure	PART 1A PF-06804103 0.15 mg/kg n=2 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.15 mg/kg on Day 1 of each 21-day cycle as an intravenous (IV) infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks. HER2 = Human Epidermal Growth Factor Receptor 2; BC = breast cancer; GC = gastric and gastroesophageal cancer.	PART 1A PF-06804103 0.5 mg/kg n=2 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.5 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 1.2 mg/kg n=2 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 1.2 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 2.0 mg/kg n=4 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 2.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 3.0 mg/kg n=16 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 4.0 mg/kg n=15 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 5.0 mg/kg n=6 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 5.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 2A PF-06804103 3.0 mg/kg HER2+ BC n=5 Participants Participants with HER2-positive BC in third line (3L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 4.0 mg/kg HER2+ BC n=14 Participants Participants with HER2-positive BC in 3L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 3.0 mg/kg HR+ HER2-Low BC n=12 Participants Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in second line (2L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks. HR = hormone receptor; IHC = immunohistochemistry; ISH = in-situ hybridization.	PART 2A PF-06804103 4.0 mg/kg HR+ HER2-Low BC n=15 Participants Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in 2L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 1B PF-06804103 2.0 mg/kg HR+ HER2-Low Combo BC n=2 Participants Postmenopausal participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC received PF-06804103 at 2.0 mg/kg once every 14 days in a 28-day cycle as an IV infusion. The maximum duration of treatment for Part 1B was approximately 53.7 weeks.
Number of Participants With Laboratory Abnormalities-Chemistries Hypophosphatemia	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	1 Participants	0 Participants	0 Participants	2 Participants	0 Participants	0 Participants
Number of Participants With Laboratory Abnormalities-Chemistries Serum amylase increased	0 Participants	0 Participants	0 Participants	0 Participants	1 Participants	0 Participants	1 Participants	0 Participants	1 Participants	0 Participants	1 Participants	0 Participants
Number of Participants With Laboratory Abnormalities-Chemistries Lipase increased	0 Participants	0 Participants	0 Participants	0 Participants	1 Participants	1 Participants	1 Participants	0 Participants	2 Participants	0 Participants	0 Participants	0 Participants
Number of Participants With Laboratory Abnormalities-Chemistries ALT increased	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	1 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants
Number of Participants With Laboratory Abnormalities-Chemistries ALP increased	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	1 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants
Number of Participants With Laboratory Abnormalities-Chemistries AST increased	0 Participants	0 Participants	0 Participants	0 Participants	1 Participants	0 Participants	1 Participants	0 Participants	0 Participants	0 Participants	1 Participants	0 Participants
Number of Participants With Laboratory Abnormalities-Chemistries Hyperglycemia	0 Participants	0 Participants	0 Participants	1 Participants	1 Participants	2 Participants	0 Participants	0 Participants	1 Participants	0 Participants	0 Participants	0 Participants
Number of Participants With Laboratory Abnormalities-Chemistries Hypermagnesemia	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	1 Participants	0 Participants
Number of Participants With Laboratory Abnormalities-Chemistries Hypocalcemia	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	1 Participants	0 Participants
Number of Participants With Laboratory Abnormalities-Chemistries Hypokalemia	1 Participants	0 Participants	1 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	1 Participants	0 Participants	1 Participants	0 Participants
Number of Participants With Laboratory Abnormalities-Chemistries Hyponatremia	0 Participants	0 Participants	0 Participants	1 Participants	0 Participants	1 Participants	2 Participants	0 Participants	3 Participants	1 Participants	0 Participants	0 Participants

PRIMARY outcome

Timeframe: From baseline to end of treatment (maximum treatment duration: 89.3 weeks for Part 1A, 49.4 weeks for Part 2A, 53.7 weeks for Part 1B)

Population: Participants who had at least one on-treatment assessment for the corresponding lab parameter.

Participants who experienced urinalysis laboratory test abnormalities were summarized according to worst toxicity grade observed for each urinalysis laboratory test. Laboratory abnormalities were graded by NCI CTCAE version 4.03 (Grade 0: no change from normal or reference range; Grade 1: mild AE; Grade 2: moderate AE; Grade 3: severe AE; Grade 4: life-threatening consequences, urgent intervention indicated). This outcome measure calculated the number of participants with urinalysis laboratory abnormalities that were shifted from \<=Grade 2 at baseline to Grade 3 or above.

Outcome measures

Outcome measures
Measure	PART 1A PF-06804103 0.15 mg/kg n=2 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.15 mg/kg on Day 1 of each 21-day cycle as an intravenous (IV) infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks. HER2 = Human Epidermal Growth Factor Receptor 2; BC = breast cancer; GC = gastric and gastroesophageal cancer.	PART 1A PF-06804103 0.5 mg/kg n=2 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.5 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 1.2 mg/kg n=2 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 1.2 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 2.0 mg/kg n=4 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 2.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 3.0 mg/kg n=14 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 4.0 mg/kg n=15 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 5.0 mg/kg n=6 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 5.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 2A PF-06804103 3.0 mg/kg HER2+ BC n=4 Participants Participants with HER2-positive BC in third line (3L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 4.0 mg/kg HER2+ BC n=3 Participants Participants with HER2-positive BC in 3L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 3.0 mg/kg HR+ HER2-Low BC n=6 Participants Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in second line (2L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks. HR = hormone receptor; IHC = immunohistochemistry; ISH = in-situ hybridization.	PART 2A PF-06804103 4.0 mg/kg HR+ HER2-Low BC n=6 Participants Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in 2L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 1B PF-06804103 2.0 mg/kg HR+ HER2-Low Combo BC Postmenopausal participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC received PF-06804103 at 2.0 mg/kg once every 14 days in a 28-day cycle as an IV infusion. The maximum duration of treatment for Part 1B was approximately 53.7 weeks.
Number of Participants With Laboratory Abnormalities-Urinalysis	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants

PRIMARY outcome

Timeframe: From baseline up to follow up (at least 28 days and no more than 35 days after discontinuation of treatment), maximum treatment duration: 89.3 weeks for Part 1A, 49.4 weeks for Part 2A, 53.7 weeks for Part 1B

Population: Participants who were evaluated against criteria.

Blood pressure (BP), including systolic BP (SBP) and diastolic BP (DBP), and pulse rate were recorded in a supine or seated position.

Outcome measures

Outcome measures
Measure	PART 1A PF-06804103 0.15 mg/kg n=2 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.15 mg/kg on Day 1 of each 21-day cycle as an intravenous (IV) infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks. HER2 = Human Epidermal Growth Factor Receptor 2; BC = breast cancer; GC = gastric and gastroesophageal cancer.	PART 1A PF-06804103 0.5 mg/kg n=2 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.5 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 1.2 mg/kg n=2 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 1.2 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 2.0 mg/kg n=4 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 2.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 3.0 mg/kg n=16 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 4.0 mg/kg n=15 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 5.0 mg/kg n=6 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 5.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 2A PF-06804103 3.0 mg/kg HER2+ BC n=5 Participants Participants with HER2-positive BC in third line (3L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 4.0 mg/kg HER2+ BC n=14 Participants Participants with HER2-positive BC in 3L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 3.0 mg/kg HR+ HER2-Low BC n=12 Participants Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in second line (2L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks. HR = hormone receptor; IHC = immunohistochemistry; ISH = in-situ hybridization.	PART 2A PF-06804103 4.0 mg/kg HR+ HER2-Low BC n=15 Participants Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in 2L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 1B PF-06804103 2.0 mg/kg HR+ HER2-Low Combo BC n=2 Participants Postmenopausal participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC received PF-06804103 at 2.0 mg/kg once every 14 days in a 28-day cycle as an IV infusion. The maximum duration of treatment for Part 1B was approximately 53.7 weeks.
Number of Participants With Vital Signs Data Meeting Pre-Defined Criteria Increase in DBP ≥20 mmHg	0 Participants	0 Participants	2 Participants	2 Participants	3 Participants	7 Participants	2 Participants	2 Participants	2 Participants	4 Participants	5 Participants	1 Participants
Number of Participants With Vital Signs Data Meeting Pre-Defined Criteria Decrease in DBP ≥20 mmHg	0 Participants	1 Participants	0 Participants	1 Participants	4 Participants	6 Participants	0 Participants	2 Participants	1 Participants	1 Participants	0 Participants	0 Participants
Number of Participants With Vital Signs Data Meeting Pre-Defined Criteria SBP value <90 mmHg	0 Participants	0 Participants	0 Participants	0 Participants	2 Participants	6 Participants	0 Participants	1 Participants	2 Participants	0 Participants	0 Participants	0 Participants
Number of Participants With Vital Signs Data Meeting Pre-Defined Criteria DBP value <50 mmHg	0 Participants	0 Participants	0 Participants	1 Participants	1 Participants	3 Participants	0 Participants	1 Participants	1 Participants	1 Participants	0 Participants	0 Participants
Number of Participants With Vital Signs Data Meeting Pre-Defined Criteria Pulse rate >120 beats per minute (bpm)	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	3 Participants	1 Participants	1 Participants	3 Participants	2 Participants	1 Participants	0 Participants
Number of Participants With Vital Signs Data Meeting Pre-Defined Criteria Increase in SBP ≥30 mmHg	0 Participants	0 Participants	2 Participants	2 Participants	2 Participants	9 Participants	1 Participants	1 Participants	3 Participants	3 Participants	4 Participants	1 Participants
Number of Participants With Vital Signs Data Meeting Pre-Defined Criteria Decrease in SBP ≥30 mmHg	0 Participants	1 Participants	0 Participants	2 Participants	4 Participants	5 Participants	0 Participants	3 Participants	1 Participants	1 Participants	1 Participants	0 Participants

PRIMARY outcome

Timeframe: Baseline, every 6 weeks from the start of treatment until disease progression, death, or permanent discontinuation of study treatment (maximum treatment duration: 49.4 weeks)

Population: Participants received at least 1 dose of study treatment with adequate baseline assessment and at least 1 determinate post baseline assessment, disease progression, or death before the first tumor assessment.

Percentage of participants with objective response based on assessment of complete response (CR) or partial response (PR) according to Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1. CR was defined as complete disappearance of all target lesions and non-target disease, with the exception of nodal disease. All nodes, both target and non-target, must decrease to normal (short axis \<10 mm). No new lesions. PR was defined as \>=30% decrease under baseline of the sum of diameters of all target lesions. The short axis was used in the sum for target nodes, while the longest diameter was used in the sum for all other target lesions. No unequivocal progression of non-target disease. No new lesions.

Outcome measures

Outcome measures
Measure	PART 1A PF-06804103 0.15 mg/kg n=4 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.15 mg/kg on Day 1 of each 21-day cycle as an intravenous (IV) infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks. HER2 = Human Epidermal Growth Factor Receptor 2; BC = breast cancer; GC = gastric and gastroesophageal cancer.	PART 1A PF-06804103 0.5 mg/kg n=11 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.5 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 1.2 mg/kg n=10 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 1.2 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 2.0 mg/kg n=11 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 2.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 3.0 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 4.0 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 5.0 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 5.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 2A PF-06804103 3.0 mg/kg HER2+ BC Participants with HER2-positive BC in third line (3L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 4.0 mg/kg HER2+ BC Participants with HER2-positive BC in 3L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 3.0 mg/kg HR+ HER2-Low BC Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in second line (2L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks. HR = hormone receptor; IHC = immunohistochemistry; ISH = in-situ hybridization.	PART 2A PF-06804103 4.0 mg/kg HR+ HER2-Low BC Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in 2L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 1B PF-06804103 2.0 mg/kg HR+ HER2-Low Combo BC Postmenopausal participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC received PF-06804103 at 2.0 mg/kg once every 14 days in a 28-day cycle as an IV infusion. The maximum duration of treatment for Part 1B was approximately 53.7 weeks.
Percentage of Participants With Objective Response in Part 2	25.0 Percentage of participants Interval 0.6 to 80.6	45.5 Percentage of participants Interval 16.7 to 76.6	10.0 Percentage of participants Interval 0.3 to 44.5	27.3 Percentage of participants Interval 6.0 to 61.0	—	—	—	—	—	—	—	—

PRIMARY outcome

Timeframe: Baseline, every 6 weeks from the start of treatment until disease progression, death, or permanent discontinuation of study treatment (maximum treatment duration: 49.4 weeks)

Duration of response (DR) was the time from first documentation of PR or CR to date of first documentation of progressive disease (PD) or death due to any cause. CR was defined as complete disappearance of all target lesions and non-target disease, with the exception of nodal disease. All nodes, both target and non-target, must decrease to normal (short axis \<10 mm). No new lesions. PR was defined as \>=30% decrease under baseline of the sum of diameters of all target lesions. The short axis was used in the sum for target nodes, while the longest diameter was used in the sum for all other target lesions. No unequivocal progression of non-target disease. No new lesions. PD was defined as at least a 20% increase (including an absolute increase of at least 5 mm) in the sum of diameters of target lesions, taking as reference the smallest sum on study and/or unequivocal progression of existing non-target lesions and/or appearance of one or more new lesions.

Outcome measures

Outcome measures
Measure	PART 1A PF-06804103 0.15 mg/kg n=1 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.15 mg/kg on Day 1 of each 21-day cycle as an intravenous (IV) infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks. HER2 = Human Epidermal Growth Factor Receptor 2; BC = breast cancer; GC = gastric and gastroesophageal cancer.	PART 1A PF-06804103 0.5 mg/kg n=5 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.5 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 1.2 mg/kg n=1 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 1.2 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 2.0 mg/kg n=3 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 2.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 3.0 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 4.0 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 5.0 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 5.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 2A PF-06804103 3.0 mg/kg HER2+ BC Participants with HER2-positive BC in third line (3L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 4.0 mg/kg HER2+ BC Participants with HER2-positive BC in 3L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 3.0 mg/kg HR+ HER2-Low BC Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in second line (2L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks. HR = hormone receptor; IHC = immunohistochemistry; ISH = in-situ hybridization.	PART 2A PF-06804103 4.0 mg/kg HR+ HER2-Low BC Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in 2L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 1B PF-06804103 2.0 mg/kg HR+ HER2-Low Combo BC Postmenopausal participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC received PF-06804103 at 2.0 mg/kg once every 14 days in a 28-day cycle as an IV infusion. The maximum duration of treatment for Part 1B was approximately 53.7 weeks.
Duration of Response (DR) in Part 2	NA Month Because there were few confirmed responders for specific treatment groups and the duration of response was censored for some participants, therefore there were insufficient number of participants with events, the estimation of median and 95% confidence intervals may not be feasible.	2.9 Month Interval 2.4 to Because there were few confirmed responders for specific treatment groups and the duration of response was censored for some participants, therefore there were insufficient number of participants with events, the estimation of median and 95% confidence intervals may not be feasible.	4 Month Because there were few confirmed responders for specific treatment groups and the duration of response was censored for some participants, therefore there were insufficient number of participants with events, the estimation of median and 95% confidence intervals may not be feasible.	NA Month Interval 4.4 to Because there were few confirmed responders for specific treatment groups and the duration of response was censored for some participants, therefore there were insufficient number of participants with events, the estimation of median and 95% confidence intervals may not be feasible.	—	—	—	—	—	—	—	—

PRIMARY outcome

Timeframe: Baseline, every 6 weeks from the start of treatment until disease progression, death, or permanent discontinuation of study treatment (maximum treatment duration: 49.4 weeks)

Population: All enrolled participants in part 2A.

Progression-free survival (PFS) was the time from randomization date to date of first documentation of PD or death due to any cause. PD was defined as at least a 20% increase (including an absolute increase of at least 5 mm) in the sum of diameters of target lesions, taking as reference the smallest sum on study and/or unequivocal progression of existing non-target lesions and/or appearance of one or more new lesions.

Outcome measures

Outcome measures
Measure	PART 1A PF-06804103 0.15 mg/kg n=5 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.15 mg/kg on Day 1 of each 21-day cycle as an intravenous (IV) infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks. HER2 = Human Epidermal Growth Factor Receptor 2; BC = breast cancer; GC = gastric and gastroesophageal cancer.	PART 1A PF-06804103 0.5 mg/kg n=14 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.5 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 1.2 mg/kg n=12 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 1.2 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 2.0 mg/kg n=15 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 2.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 3.0 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 4.0 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 5.0 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 5.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 2A PF-06804103 3.0 mg/kg HER2+ BC Participants with HER2-positive BC in third line (3L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 4.0 mg/kg HER2+ BC Participants with HER2-positive BC in 3L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 3.0 mg/kg HR+ HER2-Low BC Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in second line (2L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks. HR = hormone receptor; IHC = immunohistochemistry; ISH = in-situ hybridization.	PART 2A PF-06804103 4.0 mg/kg HR+ HER2-Low BC Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in 2L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 1B PF-06804103 2.0 mg/kg HR+ HER2-Low Combo BC Postmenopausal participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC received PF-06804103 at 2.0 mg/kg once every 14 days in a 28-day cycle as an IV infusion. The maximum duration of treatment for Part 1B was approximately 53.7 weeks.
Progression-Free Survival (PFS) in Part 2	NA Month Interval 2.6 to Because the number of participants in specific treatment groups is small and the PFS was censored for some participants, therefore there were insufficient number of participants with events, the estimation of median and 95% confidence intervals may not be feasible.	5.5 Month Interval 2.9 to Because the number of participants in specific treatment groups is small and the PFS was censored for some participants, therefore there were insufficient number of participants with events, the estimation of median and 95% confidence intervals may not be feasible.	1.3 Month Interval 0.7 to 6.4	5.6 Month Interval 2.4 to Because the number of participants in specific treatment groups is small and the PFS was censored for some participants, therefore there were insufficient number of participants with events, the estimation of median and 95% confidence intervals may not be feasible.	—	—	—	—	—	—	—	—

PRIMARY outcome

Timeframe: Baseline, every 6 weeks from the start of treatment until disease progression, death, or withdrawal from treatment (maximum treatment duration: 49.4 weeks)

Population: All enrolled participants in part 2A.

Time to progression (TTP) was the time from start date to the date of the first documentation of PD. PD was defined as at least a 20% increase (including an absolute increase of at least 5 mm) in the sum of diameters of target lesions, taking as reference the smallest sum on study and/or unequivocal progression of existing non-target lesions and/or appearance of one or more new lesions.

Outcome measures

Outcome measures
Measure	PART 1A PF-06804103 0.15 mg/kg n=5 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.15 mg/kg on Day 1 of each 21-day cycle as an intravenous (IV) infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks. HER2 = Human Epidermal Growth Factor Receptor 2; BC = breast cancer; GC = gastric and gastroesophageal cancer.	PART 1A PF-06804103 0.5 mg/kg n=14 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.5 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 1.2 mg/kg n=12 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 1.2 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 2.0 mg/kg n=15 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 2.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 3.0 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 4.0 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 5.0 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 5.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 2A PF-06804103 3.0 mg/kg HER2+ BC Participants with HER2-positive BC in third line (3L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 4.0 mg/kg HER2+ BC Participants with HER2-positive BC in 3L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 3.0 mg/kg HR+ HER2-Low BC Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in second line (2L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks. HR = hormone receptor; IHC = immunohistochemistry; ISH = in-situ hybridization.	PART 2A PF-06804103 4.0 mg/kg HR+ HER2-Low BC Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in 2L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 1B PF-06804103 2.0 mg/kg HR+ HER2-Low Combo BC Postmenopausal participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC received PF-06804103 at 2.0 mg/kg once every 14 days in a 28-day cycle as an IV infusion. The maximum duration of treatment for Part 1B was approximately 53.7 weeks.
Time to Tumor Progression (TTP) in Part 2	NA Month Interval 2.6 to Because the number of participants in specific treatment groups is small and the TTP was censored for some participants, therefore there were insufficient number of participants with events, the estimation of median and 95% confidence intervals may not be feasible.	5.5 Month Interval 2.9 to Because the number of participants in specific treatment groups is small and the TTP was censored for some participants, therefore there were insufficient number of participants with events, the estimation of median and 95% confidence intervals may not be feasible.	1.3 Month Interval 0.7 to Because the number of participants in specific treatment groups is small and the TTP was censored for some participants, therefore there were insufficient number of participants with events, the estimation of median and 95% confidence intervals may not be feasible.	5.6 Month Interval 2.4 to Because the number of participants in specific treatment groups is small and the TTP was censored for some participants, therefore there were insufficient number of participants with events, the estimation of median and 95% confidence intervals may not be feasible.	—	—	—	—	—	—	—	—

SECONDARY outcome

Timeframe: Baseline, every 6 weeks (for Part 1A) or every 8 weeks (for Part 1B) from the start of treatment until disease progression, death, or permanent discontinuation of study treatment (maximum treatment duration: 89.3 weeks for Part 1A, 53.7 weeks for Part 1B)

Outcome measures

Outcome measures
Measure	PART 1A PF-06804103 0.15 mg/kg n=6 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.15 mg/kg on Day 1 of each 21-day cycle as an intravenous (IV) infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks. HER2 = Human Epidermal Growth Factor Receptor 2; BC = breast cancer; GC = gastric and gastroesophageal cancer.	PART 1A PF-06804103 0.5 mg/kg n=4 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.5 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 1.2 mg/kg n=14 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 1.2 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 2.0 mg/kg n=14 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 2.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 3.0 mg/kg n=5 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 4.0 mg/kg n=1 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 5.0 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 5.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 2A PF-06804103 3.0 mg/kg HER2+ BC Participants with HER2-positive BC in third line (3L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 4.0 mg/kg HER2+ BC Participants with HER2-positive BC in 3L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 3.0 mg/kg HR+ HER2-Low BC Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in second line (2L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks. HR = hormone receptor; IHC = immunohistochemistry; ISH = in-situ hybridization.	PART 2A PF-06804103 4.0 mg/kg HR+ HER2-Low BC Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in 2L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 1B PF-06804103 2.0 mg/kg HR+ HER2-Low Combo BC Postmenopausal participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC received PF-06804103 at 2.0 mg/kg once every 14 days in a 28-day cycle as an IV infusion. The maximum duration of treatment for Part 1B was approximately 53.7 weeks.
Percentage of Participants With Objective Response in Part 1	16.7 Percentage of participants Interval 0.4 to 64.1	0 Percentage of participants Interval 0.0 to 60.2	21.4 Percentage of participants Interval 4.7 to 50.8	42.9 Percentage of participants Interval 17.7 to 71.1	60.0 Percentage of participants Interval 14.7 to 94.7	100.0 Percentage of participants Interval 2.5 to 100.0	—	—	—	—	—	—

SECONDARY outcome

Outcome measures

Outcome measures
Measure	PART 1A PF-06804103 0.15 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.15 mg/kg on Day 1 of each 21-day cycle as an intravenous (IV) infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks. HER2 = Human Epidermal Growth Factor Receptor 2; BC = breast cancer; GC = gastric and gastroesophageal cancer.	PART 1A PF-06804103 0.5 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.5 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 1.2 mg/kg n=1 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 1.2 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 2.0 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 2.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 3.0 mg/kg n=3 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 4.0 mg/kg n=6 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 5.0 mg/kg n=3 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 5.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 2A PF-06804103 3.0 mg/kg HER2+ BC n=1 Participants Participants with HER2-positive BC in third line (3L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 4.0 mg/kg HER2+ BC Participants with HER2-positive BC in 3L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 3.0 mg/kg HR+ HER2-Low BC Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in second line (2L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks. HR = hormone receptor; IHC = immunohistochemistry; ISH = in-situ hybridization.	PART 2A PF-06804103 4.0 mg/kg HR+ HER2-Low BC Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in 2L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 1B PF-06804103 2.0 mg/kg HR+ HER2-Low Combo BC Postmenopausal participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC received PF-06804103 at 2.0 mg/kg once every 14 days in a 28-day cycle as an IV infusion. The maximum duration of treatment for Part 1B was approximately 53.7 weeks.
Duration of Response (DR) in Part 1	—	—	4.2 Month Because there were no or few confirmed responders for specific treatment groups and the duration of response was censored for some participants, therefore there were insufficient number of participants with events, the estimation of median and 95% confidence intervals may not be feasible.	—	15.5 Month Interval 6.0 to 18.9	7.3 Month Interval 5.5 to 18.7	NA Month Because there were no or few confirmed responders for specific treatment groups and the duration of response was censored for some participants, therefore there were insufficient number of participants with events, the estimation of median and 95% confidence intervals may not be feasible.	NA Month Because there were no or few confirmed responders for specific treatment groups and the duration of response was censored for some participants, therefore there were insufficient number of participants with events, the estimation of median and 95% confidence intervals may not be feasible.	—	—	—	—

SECONDARY outcome

Population: All enrolled participants in part 1.

Outcome measures

Outcome measures
Measure	PART 1A PF-06804103 0.15 mg/kg n=6 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.15 mg/kg on Day 1 of each 21-day cycle as an intravenous (IV) infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks. HER2 = Human Epidermal Growth Factor Receptor 2; BC = breast cancer; GC = gastric and gastroesophageal cancer.	PART 1A PF-06804103 0.5 mg/kg n=4 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.5 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 1.2 mg/kg n=16 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 1.2 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 2.0 mg/kg n=15 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 2.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 3.0 mg/kg n=6 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 4.0 mg/kg n=2 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 5.0 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 5.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 2A PF-06804103 3.0 mg/kg HER2+ BC Participants with HER2-positive BC in third line (3L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 4.0 mg/kg HER2+ BC Participants with HER2-positive BC in 3L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 3.0 mg/kg HR+ HER2-Low BC Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in second line (2L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks. HR = hormone receptor; IHC = immunohistochemistry; ISH = in-situ hybridization.	PART 2A PF-06804103 4.0 mg/kg HR+ HER2-Low BC Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in 2L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 1B PF-06804103 2.0 mg/kg HR+ HER2-Low Combo BC Postmenopausal participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC received PF-06804103 at 2.0 mg/kg once every 14 days in a 28-day cycle as an IV infusion. The maximum duration of treatment for Part 1B was approximately 53.7 weeks.
Progression-Free Survival (PFS) in Part 1	4.2 Month Interval 0.7 to 15.7	3.4 Month Interval 2.6 to Because the number of participants in specific treatment groups is small and the PFS was censored for some participants, therefore there were insufficient number of participants with events, the estimation of median and 95% confidence intervals may not be feasible.	4.7 Month Interval 1.2 to 7.2	8.2 Month Interval 4.3 to 14.9	NA Month Interval 2.7 to Because the number of participants in specific treatment groups is small and the PFS was censored for some participants, therefore there were insufficient number of participants with events, the estimation of median and 95% confidence intervals may not be feasible.	NA Month Because the number of participants in specific treatment groups is small and the PFS was censored for some participants, therefore there were insufficient number of participants with events, the estimation of median and 95% confidence intervals may not be feasible.	—	—	—	—	—	—

SECONDARY outcome

Population: All enrolled participants in part 1.

Outcome measures

Outcome measures
Measure	PART 1A PF-06804103 0.15 mg/kg n=6 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.15 mg/kg on Day 1 of each 21-day cycle as an intravenous (IV) infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks. HER2 = Human Epidermal Growth Factor Receptor 2; BC = breast cancer; GC = gastric and gastroesophageal cancer.	PART 1A PF-06804103 0.5 mg/kg n=4 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.5 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 1.2 mg/kg n=16 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 1.2 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 2.0 mg/kg n=15 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 2.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 3.0 mg/kg n=6 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 4.0 mg/kg n=2 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 5.0 mg/kg Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 5.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 2A PF-06804103 3.0 mg/kg HER2+ BC Participants with HER2-positive BC in third line (3L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 4.0 mg/kg HER2+ BC Participants with HER2-positive BC in 3L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 3.0 mg/kg HR+ HER2-Low BC Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in second line (2L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks. HR = hormone receptor; IHC = immunohistochemistry; ISH = in-situ hybridization.	PART 2A PF-06804103 4.0 mg/kg HR+ HER2-Low BC Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in 2L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 1B PF-06804103 2.0 mg/kg HR+ HER2-Low Combo BC Postmenopausal participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC received PF-06804103 at 2.0 mg/kg once every 14 days in a 28-day cycle as an IV infusion. The maximum duration of treatment for Part 1B was approximately 53.7 weeks.
Time to Tumor Progression (TTP) in Part 1	4.2 Month Interval 0.7 to 15.7	3.4 Month Interval 2.6 to Because the number of participants in specific treatment groups is small and the TTP was censored for some participants, therefore there were insufficient number of participants with events, the estimation of median and 95% confidence intervals may not be feasible.	4.7 Month Interval 1.2 to 7.2	8.2 Month Interval 4.3 to 14.9	NA Month Interval 2.7 to Because the number of participants in specific treatment groups is small and the TTP was censored for some participants, therefore there were insufficient number of participants with events, the estimation of median and 95% confidence intervals may not be feasible.	NA Month Because the number of participants in specific treatment groups is small and the TTP was censored for some participants, therefore there were insufficient number of participants with events, the estimation of median and 95% confidence intervals may not be feasible.	—	—	—	—	—	—

SECONDARY outcome

Timeframe: Prior to the start of treatment on Day 1 of Cycle 1 up to end of treatment (maximum treatment duration: 89.3 weeks for Part 1A, 49.4 weeks for Part 2A, 53.7 weeks for Part 1B)

Population: All enrolled participants who received at least one dose of study treatment and had at least 1 ADA sample collected.

To evaluate the immunogenicity as measured by presence of ADA and NAb in participants treated with PF-06804103.

Outcome measures

Outcome measures
Measure	PART 1A PF-06804103 0.15 mg/kg n=2 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.15 mg/kg on Day 1 of each 21-day cycle as an intravenous (IV) infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks. HER2 = Human Epidermal Growth Factor Receptor 2; BC = breast cancer; GC = gastric and gastroesophageal cancer.	PART 1A PF-06804103 0.5 mg/kg n=2 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.5 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 1.2 mg/kg n=2 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 1.2 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 2.0 mg/kg n=4 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 2.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 3.0 mg/kg n=12 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 4.0 mg/kg n=15 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 5.0 mg/kg n=6 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 5.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 2A PF-06804103 3.0 mg/kg HER2+ BC n=5 Participants Participants with HER2-positive BC in third line (3L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 4.0 mg/kg HER2+ BC n=13 Participants Participants with HER2-positive BC in 3L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 3.0 mg/kg HR+ HER2-Low BC n=10 Participants Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in second line (2L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks. HR = hormone receptor; IHC = immunohistochemistry; ISH = in-situ hybridization.	PART 2A PF-06804103 4.0 mg/kg HR+ HER2-Low BC n=15 Participants Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in 2L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 1B PF-06804103 2.0 mg/kg HR+ HER2-Low Combo BC n=2 Participants Postmenopausal participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC received PF-06804103 at 2.0 mg/kg once every 14 days in a 28-day cycle as an IV infusion. The maximum duration of treatment for Part 1B was approximately 53.7 weeks.
Number of Participants With Anti-Drug Antibodies (ADA) and Neutralizing Antibody (NAb) Against PF-06804103 Participants with ADA	0 Participants	0 Participants	1 Participants	0 Participants	2 Participants	2 Participants	0 Participants	0 Participants	2 Participants	4 Participants	5 Participants	0 Participants
Number of Participants With Anti-Drug Antibodies (ADA) and Neutralizing Antibody (NAb) Against PF-06804103 Participants with NAb	0 Participants	0 Participants	1 Participants	0 Participants	1 Participants	0 Participants	0 Participants	0 Participants	0 Participants	0 Participants	2 Participants	0 Participants

SECONDARY outcome

Timeframe: Baseline

Population: All enrolled participants with at least 1 of the biomarkers evaluated at pre- and/or post-dose.

Tumor tissues from archived tissue biopsy were analyzed for HER2 mutations.

Outcome measures

Outcome measures
Measure	PART 1A PF-06804103 0.15 mg/kg n=2 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.15 mg/kg on Day 1 of each 21-day cycle as an intravenous (IV) infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks. HER2 = Human Epidermal Growth Factor Receptor 2; BC = breast cancer; GC = gastric and gastroesophageal cancer.	PART 1A PF-06804103 0.5 mg/kg n=2 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 0.5 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 1.2 mg/kg n=2 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 1.2 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 2.0 mg/kg n=4 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 2.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 3.0 mg/kg n=14 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 4.0 mg/kg n=15 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 1A PF-06804103 5.0 mg/kg n=6 Participants Participants with HER2-positive BC or HER2-positive GC received PF-06804103 at 5.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 1A was approximately 89.3 weeks.	PART 2A PF-06804103 3.0 mg/kg HER2+ BC n=5 Participants Participants with HER2-positive BC in third line (3L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 4.0 mg/kg HER2+ BC n=14 Participants Participants with HER2-positive BC in 3L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 2A PF-06804103 3.0 mg/kg HR+ HER2-Low BC n=12 Participants Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in second line (2L) setting received PF-06804103 at 3.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks. HR = hormone receptor; IHC = immunohistochemistry; ISH = in-situ hybridization.	PART 2A PF-06804103 4.0 mg/kg HR+ HER2-Low BC n=15 Participants Participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC in 2L setting received PF-06804103 at 4.0 mg/kg on Day 1 of each 21-day cycle as an IV infusion. The maximum duration of treatment for Part 2A was approximately 49.4 weeks.	PART 1B PF-06804103 2.0 mg/kg HR+ HER2-Low Combo BC n=2 Participants Postmenopausal participants with HR-positive HER2 IHC 1+ or IHC 2+/ISH- BC received PF-06804103 at 2.0 mg/kg once every 14 days in a 28-day cycle as an IV infusion. The maximum duration of treatment for Part 1B was approximately 53.7 weeks.
Number of Participants With HER2 Positivity Based on Tumor Tissue Analysis	2 Participants	2 Participants	1 Participants	3 Participants	10 Participants	13 Participants	6 Participants	5 Participants	14 Participants	4 Participants	1 Participants	0 Participants

SECONDARY outcome

Timeframe: Pre-dose, 1, 4, 24, 72, 168, 336 hours post-dose of Cycle 1 & 4 Day 1 for Part 1A; pre-dose, 1, 4, 24, 72, 168 hours post-dose of Cycle 1 & 4 Day 1 for Part 1B