CStone’s CS2009 trispecific antibody reinforces three clinical validations at ESMO

With data from over 300 patients across multiple tumor types and Phase 3 trials coming soon, the evidence supports CS2009’s mechanism, safety and antitumor efficacy

Key Takeaways:

• CS2009 delivered strong efficacy data in both monotherapy and combination regimens for non-small cell lung cancer and metastatic colorectal cancer
• Clinical data from over 300 patients across multiple solid tumors for the trispecific antibody support validation for proof of mechanism, safety and concept

By Molly Wen

In the world of high-tech treatments targeting specific vulnerabilities on cancer cells, one or two lines of attack aren’t as good as three. CStone Pharmaceuticals (2616.HK) is well aware of that, and made headlines last week with new research showing its self-developed PD-1/VEGF/CTLA-4 trispecific antibody CS2009 is making significant clinical progress for the treatment of multiple types of cancer.

The drug has now amassed clinical data from over 300 patients, further validating its mechanism of action, safety and antitumor activity across various solid tumors, CStone said at the 2026 European Society for Medical Oncology (ESMO) Congress. Its addressable market includes patients previously treated with immunotherapy, as well as those with “cold tumors” for whom traditional immunotherapies offer limited efficacy.

The latest results mark CS2009’s transition from early clinical exploration to the pivotal efficacy validation phase. The therapeutic potential of its design is now being backed by an increasingly strong body of clinical data, and CStone plans to begin global Phase 3 trials by year-end, advancing the drug into late-stage development as it works toward potential regulatory approval.

The development goal for CS2009 is not a simple combination of three mature targets, said Dr. Jason Yang, CStone’s CEO and president of R&D. Instead, CS2009 is designed to engage three complementary mechanisms at once: CTLA-4 blockade to enhance T-cell priming and expansion, PD-1 blockade to restore the function of exhausted T cells, and VEGFA blockade to normalize tumor vasculature and counteract immunosuppression.

Immunotherapies represented by PD-1/PD-L1 have been widely adopted to treat multiple cancer types in recent years, including lung, melanoma and kidney cancer. But some patients still experience limited benefits or develop resistance post-treatment. CS2009 is notable for targeting PD-1, VEGF, and CTLA-4 simultaneously. PD-1 aims to restore the anti-tumor capacity of immune cells; targeting VEGF attacks the ability of tumors to create new blood vessels; while blocking CTLA-4 helps activate the immune system at an earlier stage.

However, CTLA-4-related drugs can trigger severe immune side effects, curtailing their clinical use. To address this, CStone utilized a specialized molecular design in an effort to enhance the drug’s activity in the tumor and surrounding tissue while minimizing its impact on normal tissue. The latest clinical data indicate that CS2009 effectively engages its three preset targets, validating the scientific rationale behind its innovative design and providing a research foundation for further elevating treatment efficacy.

Safety remains a major hurdle for multi-target immunotherapies, particularly given the inclusion of the CTLA-4 target in CS2009. The new data shows the incidence rates of Grade 3 and above immune-related adverse events in NSCLC patients were 11.6% for CS2009 monotherapy and 12.7% for its combination with chemotherapy. The study detected no new safety signals, nor did it observe a clear superimposition of immune-related or VEGF-related toxicities following combination chemotherapy. This implies that CS2009 is achieving sustained inhibition of all three pathways while maintaining a manageable safety profile.

Clinical efficacy validation

In terms of therapeutic efficacy, CS2009 first delivered positive results as a first-line monotherapy for NSCLC. For patients with high PD-L1 expression, its objective response rate (ORR) reached 87.5%, meaning 21 out of 24 patients achieved an objective response; notably, all the 11 patients in the 30 mg/kg dose cohort achieved an objective response, equal to an ORR of 100%. Across the broader spectrum of PD-L1-positive patients, the objective response rate came in at 66.7%.

PD-L1 expression levels serve as a critical reference metric for physicians when selecting NSCLC immunotherapy regimens. Typically, patients with high expression have a greater chance of benefiting from immunotherapy alone, whereas those with lower expression often require combination with chemotherapy. Consequently, whether CS2009 can consistently yield positive outcomes in patients across varying expression levels remains a focal point for future clinical research.

In NSCLC combination therapy, CS2009 plus chemotherapy achieved an objective response rate of 81.5% in first-line squamous NSCLC, with all 27 patients achieving disease control. Within this group, all 8 PD-L1-negative patients (TPS <1%) achieved an objective response, for an ORR of 100%. For second- and third-line NSCLC patients who had previously received immunotherapy and platinum-based chemotherapy, CS2009 combined with docetaxel attained a response rate of 55.6%, leading to disease control in all 18 patients. That shows CS2009 could provide a new therapeutic avenue for patients who have failed prior treatments.

In the first-line treatment of colorectal cancer, the objective response rate for CS2009 combined with chemotherapy reached 63.6%, including a 68.8% response rate among patients with liver metastases. For the majority of colorectal cancer patients who traditionally see limited benefits from immunotherapy, these findings furnish preliminary evidence for broadening the clinical use of immunotherapy.

Anti-tumor activity was also observed with CS2009 monotherapy in refractory patients who had undergone multiple lines of prior treatment. Specifically, NSCLC patients registered a response rate of 28% in the 30 mg/kg cohort, with a median duration of response hitting 10.5 months; in patients with microsatellite stable metastatic colorectal cancer, who generally respond poorly to conventional immunotherapy, the monotherapy response rate was 20%, alongside a disease control rate reaching 93.3%.

Beyond these two primary cancer types, CStone has also observed preliminary anti-tumor activity across a variety of solid tumors using CS2009, including soft tissue sarcoma, non-clear cell renal cell carcinoma, small cell lung cancer, ovarian cancer, hepatocellular carcinoma, gastric cancer, esophageal cancer, metastatic castration-resistant prostate cancer, and triple-negative breast cancer. Detailed data were not disclosed in the ESMO presentations.

Overall, CS2009 has notched positive results across front-line and later-line settings, as well as in monotherapy and combination treatments for various cancers. The therapy’s underlying value extends beyond simply ameliorating the limitations of existing immunotherapies; it is also expected to widen the eligible patient population for immunotherapy and emerge as a next-generation anti-tumor drug that can be paired with current regimens such as chemotherapy.

At present, several pharmaceutical companies globally are advancing PD-1/VEGF/CTLA-4 trispecific antibodies, with CS2009 positioned as one of the frontrunners. Some dual-target drugs have already made headway in terms of commercialization. Akeso (9926.HK) secured Chinese market approval for its PD-1/VEGF bispecific antibody Ivonescimab in 2024; and in June 2025, Bristol-Myers Squibb (BMY.US) reached a global partnership agreement with BioNTech (BNTX.US) for the PD-L1/VEGF bispecific antibody BNT327, boasting a total potential deal value of $11.1 billion. These milestones underscore the intense focus of multinational pharma giants on this technological pathway and provide a commercial benchmark for CS2009’s future quest for overseas out-licensing.

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