CStone initiates global phase 2 trial for CS2009

CStone Pharmaceuticals announced on September 23, 2025, the enrollment of the first patient in Australia for its global multicenter phase 2 clinical trial of CS2009, a PD-1/VEGF/CTLA-4 trispecific antibody. Enrollment is currently ongoing in Australia and China, with planned expansion to the United States. This trial aims to evaluate the safety, tolerability, PK/PD profile, and efficacy of CS2009 as both monotherapy and in combination regimens across 15 cohorts covering multiple solid tumor indications.

The initiation follows promising results from a phase 1 dose-escalation study, where CS2009 demonstrated favorable safety with no dose-limiting toxicities, good tolerability, and pharmacokinetics/pharmacodynamics consistent with expectations, supporting every-three-week dosing. The phase 1 study also showed broad and deepening antitumor activity across all doses and various tumor types, including cold tumors and PD-(L)1-refractory/resistant patients.

Full phase 1 clinical data for CS2009 are scheduled for presentation at the European Society for Medical Oncology (ESMO) Congress in October 2025. CS2009 is a novel trispecific antibody developed by CStone, designed to achieve multidimensional antitumor effects by targeting PD-1, VEGFA, and CTLA-4.