CStone Pharmaceuticals (HKEX:2616), a China-based biopharmaceutical company focused on the research and development of therapies for oncology, autoimmune/inflammation, and other key disease areas, announced on Sunday the first disclosure of preliminary Phase I data for CS2009 (a PD-1/VEGF/CTLA-4 trispecific antibody) at the 2025 European Society for Medical Oncology (ESMO) Annual Congress.

According to CStone, this represents the first known clinical data publication of a PD-1/VEGF/CTLA-4 trispecific antibody to date.

The multi-regional phase I study in Australia and China is evaluating the safety, tolerability, pharmacokinetics (PK)/pharmacodynamics (PD), and anti-tumour activity of CS2009 in patients with advanced solid tumours. As of the data cutoff date, 72 patients with advanced solid tumours were treated across six dose levels (DL1-6, 1-45 mg/kg), and 72.2% remain on treatment.

Over 51% had previously received immuno-oncology (IO) therapies. The median follow-up was only 1.9 months (range 0.1 to 6.7 months) at data cutoff.

CStone reported favourable safety and tolerability: dose escalation was completed with no dose-limiting toxicity reported and the maximum tolerated dose was not reached.

As of the cutoff date, the overall follow-up duration remained limited, particularly in higher-dose cohorts where the majority of patients had yet to reach the protocol-specified time point of post-baseline tumour assessment. Data shows that 49/72 patients underwent at least one post-baseline tumour assessment by data cutoff. Despite limited follow-up duration, anti-tumour activity was observed across all dose levels with dose-dependent uptrend, and promising efficacy signals were observed across multiple tumour types.

CStone has initiated a Phase II dose expansion study in first-line patients with selected tumour types for dose optimisation and to generate data supporting registration trials in first-line NSCLC and other tumours as monotherapy or in combination therapies.