CStone Pharmaceuticals Receives FDA Clearance for CS2009 Phase II Trial in Solid Tumors

CStone Pharmaceuticals has received US Food and Drug Administration clearance for its investigational new drug application, enabling the company to initiate a Phase II clinical trial of CS2009, its trispecific antibody, in patients with advanced solid tumors. The FDA clearance expands an ongoing global multicenter study.

The ongoing global trial uses a parallel, multi-cohort expansion design. It will examine the safety, efficacy, pharmacokinetics and tolerability of CS2009 as both monotherapy and in combination regimens. Recruitment is ongoing in China and Australia, with IND clearance now obtained in the US.

A total of 15 cohorts are planned across nine solid tumor indications, including cervical cancer, extensive-stage small cell lung cancer, gastric or gastroesophageal junction cancer, ovarian cancer, and triple-negative breast cancer. The trial also includes non-small cell lung cancer, colorectal cancer, hepatocellular carcinoma, and esophageal squamous cell carcinoma.

CS2009 is an antibody targeting programmed cell death protein 1 (PD-1), vascular endothelial growth factor A (VEGFA), and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4). According to CStone, it is designed to deliver anti-tumour effects on multiple fronts by combining three clinically validated targets within a single agent.

Mechanistically, PD-1 blockade is intended to reverse T cell exhaustion, CTLA-4 inhibition promotes T cell activation and proliferation, and VEGFA targeting suppresses tumor angiogenesis while potentially improving immune cell infiltration within the tumor microenvironment. According to the company, crosslinking with VEGFA enhances checkpoint inhibition activity within tumors, while preferential targeting of PD-1 and CTLA-4 on double-positive tumor-infiltrating T cells may reduce peripheral immune interference.

The CEO, R&D president and executive director stated: "This milestone follows a productive interaction with the agency, during which they reviewed our comprehensive Phase I data, including safety and anti-tumour activity data collected during dose escalation and expansion, and provided alignment on key elements of the Phase II study design, including dose optimisation and expansion strategies. We are now actively advancing the CS2009 clinical programme globally and look forward to sharing further updates as the study progresses."

Initial Phase I data, which the company previously presented at the 2025 European Society for Medical Oncology annual meeting, demonstrated a favorable safety profile with encouraging antitumor activity during dose-escalation and expansion phases. Additional data from Phase I and ongoing Phase II cohorts are expected to be presented at upcoming American Society of Clinical Oncology and European Society for Medical Oncology meetings later in 2026.

In March 2025, CStone dosed the first subject in the multi-centre Phase I trial of CS2009.

The FDA clearance comes as CStone's share price sits at HK$5.91, with a 7 day share price return of 14.98% and a 1 year total shareholder return of 113.36%. The company's P/S ratio of 38x at a share price of HK$5.91 is above both the Hong Kong Biotechs industry average of 14.2x and a peer average of 25.4x. The company currently has a net loss of CN¥377.089m.