CStone Receives FDA Clearance to Advance CS2009 Trispecific Antibody to Phase II Trials
The FDA has cleared CStone Pharmaceuticals' investigational new drug application to begin a Phase II trial of its trispecific antibody CS2009 in advanced solid tumors. The multicenter trial will evaluate monotherapy and combination regimens across nine cancer types in Australia, China, and the U.S. Initial Phase I data showed a favorable safety profile and encouraging antitumor activity.
CStone Pharmaceuticals has received clearance from the U.S. Food and Drug Administration to initiate a Phase II clinical trial for its investigational trispecific antibody, CS2009. The trial will evaluate the therapy in patients with advanced solid tumors.
The global, multicenter Phase II study is currently enrolling patients in Australia and China. The trial design includes 15 cohorts evaluating CS2009 as both monotherapy and combination regimens across nine solid tumor indications. These indications include non-small cell lung cancer, colorectal cancer, triple-negative breast cancer, extensive-stage small cell lung cancer, platinum-resistant ovarian cancer, cervical cancer, hepatocellular carcinoma, gastric or gastroesophageal junction cancer, and esophageal squamous cell carcinoma.
CS2009 is designed to target PD-1, VEGFA, and CTLA-4 simultaneously. According to the company, the antibody combines three clinically validated targets to exert multidimensional anti-tumor effects through synergistic actions. It is designed to preferentially block PD-1 and CTLA-4 on double-positive tumor-infiltrating T cells while minimizing interference with CTLA-4 regulation in peripheral T cells.
Initial Phase I data for CS2009, previously presented at the 2025 European Society for Medical Oncology annual meeting, demonstrated a favorable safety profile with encouraging antitumor activities. The company stated that further clinical data from both the Phase I and II studies is expected to be disclosed at the upcoming American Society of Clinical Oncology and ESMO congresses later this year.
The company's CEO and President of R&D stated that the FDA clearance followed a productive interaction where the agency reviewed comprehensive Phase I data—including safety and antitumor activity data collected during dose escalation and expansion—and provided alignment on key elements of the Phase II study design, including dose optimization and expansion strategies.
CStone, established in late 2015, is focused on the research and development of therapies for oncology, autoimmune/inflammation, and other key disease areas. To date, the company has launched 4 innovative drugs and secured approvals for 20 new drug applications covering 9 indications. Its pipeline includes 16 promising candidates.