SUZHOU, China, June 1, 2026
CStone Pharmaceuticals announced updated clinical data for CS2009, its investigational PD-1/VEGF/CTLA-4 trispecific antibody, at the 2026 American Society of Clinical Oncology (ASCO) Annual Meeting, highlighting promising efficacy across multiple solid tumors and reinforcing the therapeutic potential of its triple-target mechanism. The latest Phase I/II results demonstrated robust antitumor activity in both first-line and later-line treatment settings, including non-small cell lung cancer (NSCLC) and metastatic colorectal cancer (mCRC).
The data provide growing evidence that CS2009 may help address major challenges in cancer immunotherapy, including treatment resistance and limited responses in immunologically “cold” tumors. Company leadership described the findings as a significant proof-of-concept milestone supporting future global registrational development.
Impressive Responses Reported in First-Line and Resistant NSCLC
CStone reported particularly strong outcomes in first-line NSCLC patients with high PD-L1 expression. Among patients with PD-L1 tumor proportion scores of at least 50%, CS2009 monotherapy achieved an objective response rate (ORR) of 81.3% and a disease control rate (DCR) of 100%, with consistent activity observed in both squamous and non-squamous disease. In first-line squamous NSCLC patients with low or negative PD-L1 expression, CS2009 combined with chemotherapy generated a 75% ORR and 100% DCR, while PD-L1-negative patients achieved a remarkable 100% ORR.
In heavily pretreated later-line NSCLC patients, including those previously treated with immunotherapy and platinum-based chemotherapy, the therapy continued to demonstrate durable tumor shrinkage, with a 6-month duration of response rate of 85.7%, highlighting its potential to overcome immunotherapy resistance.
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Encouraging Activity Expands into Colorectal Cancer and Cold Tumors
The trispecific antibody also demonstrated meaningful activity in colorectal cancer and several traditionally immunotherapy-resistant tumor types. In heavily pretreated patients with pMMR/MSS metastatic colorectal cancer, CS2009 monotherapy achieved an ORR of 25% and a DCR of 87.5%. When combined with XELOX chemotherapy in first-line colorectal cancer patients, the therapy produced an ORR of 66.7% and a DCR of 100%.
Additional antitumor activity was observed in soft tissue sarcoma and non-clear cell renal cell carcinoma, where ORRs reached 33.3% in both indications. These findings support the hypothesis that simultaneous inhibition of PD-1, VEGF, and CTLA-4 can remodel the tumor microenvironment and extend immunotherapy benefits into patient populations that historically have shown limited responses to checkpoint inhibitors.
Favorable Safety Profile Supports Global Phase III Development
Updated safety analyses from nearly 300 patients enrolled across China and Australia confirmed a manageable tolerability profile for CS2009. The incidence of Grade 3 or higher treatment-related adverse events remained relatively low, while immune-related toxicities were manageable and no unexpected safety concerns emerged during extended follow-up. Importantly, dose-escalation studies completed without identifying a maximum tolerated dose, further supporting the drug’s development potential. Pharmacokinetic and pharmacodynamic analyses demonstrated strong receptor occupancy, durable VEGF suppression, and robust T-cell activation, validating the intended triple-target mechanism.
With U.S. IND clearance secured and Phase II expansion studies ongoing, CStone plans to initiate its first global Phase III multi-regional registrational trial by the end of 2026, positioning CS2009 as a potential next-generation immunotherapy platform for lung cancer, colorectal cancer, and other advanced solid tumors.
Source: CStone Pharmaceuticals press release
