CStone Updated Clinical Progress and Key Phase I/II Data for CS2009 (PD-1/VEGF/CTLA-4 Trispecific Antibody)

Key Highlights:

• Excellent Safety Profile:  As of mid-March 2026, 113 heavily pretreated patients with solid tumors have been enrolled in the Phase I trial of CS2009, with a median follow-up of approximately 6 months. The more mature data continue to show a favorable safety profile, with 23% incidence of Grade ≥3 Treatment-Related Adverse Events (TRAEs). No excessive toxicities that typically occurred in combination therapies containing CTLA-4 and PD-(L)1 were observed, and the incidence of Grade ≥3 VEGF-related AEs was low.
• Compelling Efficacy in Lung Cancer: CS2009 monotherapy demonstrates potentially transformative Phase I/II efficacy in Non-Small Cell Lung Cancer (NSCLC). In first-line NSCLC (PD-L1 tumor proportion score [TPS]≥50%), the overall response rate (ORR) reached 90%, with a disease control rate (DCR) of 100%. In AGA-negative, later-line NSCLC, ORR reached 25%.
• Broad Antitumor Potential, Including in "Cold Tumors": CS2009 monotherapy also demonstrates potent antitumor activity in later-line "cold" tumors that are not sensitive to PD-(L)1 mAb. An ORR of 40% was observed in patients with non-clear cell renal cell carcinoma (nccRCC), and an ORR of 33.3% in soft tissue sarcoma (STS), demonstrating its broad-spectrum therapeutic potential across multiple tumor types.
• Accelerated Global Phase III Development Plan: The company plans to initiate the first wave of Phase III global multi-regional clinical trials (MRCT) for CS2009 by the end of 2026, targeting indications including NSCLC, colorectal cancer (CRC), and small cell lung cancer (SCLC).
• Data Presentation Plan: Updated Phase I and Phase II clinical data for CS2009 are expected to be disclosed at the 2026 American Society of Clinical Oncology (ASCO) Annual Meeting and/or the European Society for Medical Oncology (ESMO) Congress.

SUZHOU, China, March 26, 2026 /PRNewswire/ -- CStone Pharmaceuticals (HKEX: 2616), an innovation-driven biopharmaceutical company focused on the research and development of therapeutics for oncology, immunology, inflammation, and other key disease areas, today announced encouraging clinical progress for CS2009, a novel PD-1/VEGF/CTLA-4 trispecific antibody.

Dr. Jason Yang, CEO, President of R&D, and Executive Director at CStone, stated, "Based on the latest clinical data for CS2009, we are confident in its potential to transform treatment paradigms across a broad spectrum of tumor types. Driven by its unique molecular design, CS2009 offers key mechanistic differentiation. To date, approximately 200 patients have been enrolled, demonstrating an outstanding safety profile with no observation of the severe toxicities commonly associated with combination regimens containing CTLA-4 and PD-(L)1 inhibitors.

In terms of efficacy, CS2009 has delivered compelling results across multiple indications: as a monotherapy in first-line NSCLC, it achieved an ORR of 90% in patients with PD-L1 TPS ≥ 50%. Significant benefits were also observed in historically difficult-to-treat 'cold tumors', including IO-pretreated advanced NSCLC, non-clear cell renal cell carcinoma (nccRCC), and soft tissue sarcoma (STS). Furthermore, Phase II studies evaluating CS2009 in combination with standard chemotherapy for first-line NSCLC, CRC, and other indications have yielded high objective response rates.

We look forward to presenting additional Phase I and Phase II data at this year's ASCO and/or ESMO congresses. Currently, we are engaged in advanced partnership discussions with several global multinational pharmaceutical companies and aim to initiate multiple Phase III MRCT by the end of 2026."

Rapid Patient Enrollment with Phase I/II Data Supporting Favorable Safety and Efficacy

The global multi-center Phase I/II clinical trial for CS2009 is actively ongoing in Australia and China, and its Investigational New Drug (IND) application for Phase II has been approved by the U.S. Food and Drug Administration (FDA). As of mid-March 2026, a total of 113 patients with advanced solid tumors have been enrolled in Phase I, with a median follow-up of approximately six months. 85 patients have been enrolled in Phase II.

1. Phase I Data Reinforces an Excellent Safety Profile:

• CS2009 demonstrates a favorable safety and tolerability profile across all six dose levels evaluated, with no dose-limiting toxicities (DLTs) observed and the maximum tolerated dose (MTD) not reached.
• The incidence of Grade ≥3 TRAEs was 23%; Grade ≥3 immune-related adverse events (irAEs) was 12.4%; and Grade ≥3 VEGF-related TRAEs was 4.4%. No excessive toxicities that typically occurred in combination therapies containing CTLA-4 and PD-(L)1 were observed.

2. Broad Antitumor Activity Observed in Heavily-Pretreated NSCLC and "Cold Tumors":
Antitumor activity was observed across all dose levels, with robust efficacy signals in multiple tumor types.

• At the 30 mg/kg, Q3W, CS2009 monotherapy achieved an ORR of 25% (6/24) and a DCR of 58.3% (14/24) in AGA-negative, later-line NSCLC patients.

• Across dose levels, CS2009 monotherapy resulted in an ORR of 40% and a DCR of 100% in patients with nccRCC (n=5).
• Across dose levels, CS2009 monotherapy resulted in an ORR of 33.3% and a DCR of 66.7% in patients with STS (n=9).

Phase II Data Reveal Transformative Potential of CS2009: 90% ORR with Monotherapy in First-Line NSCLC and Excellent Tolerability in Combination Regimens for First-Line NSCLC and CRC

The global multi-center Phase II clinical trial employs a multi-cohort parallel expansion design to evaluate the efficacy and safety of CS2009 monotherapy and combination therapy across 15 cohorts in 9 solid tumor types, including NSCLC, CRC, extensive-stage small cell lung cancer (ES-SCLC), cervical cancer (CC), gastric or gastroesophageal junction cancer (GC/GEJC), esophageal squamous cell carcinoma (ESCC), platinum-resistant ovarian cancer (PROC), triple-negative breast cancer (TNBC), and hepatocellular carcinoma (HCC).

1. Monotherapy Shows Striking Efficacy in First-line NSCLC:
CS2009 monotherapy (20 mg/30 mg, Q3W) achieved an ORR of 90% (9/10) and a DCR of 100% (10/10) in first-line NSCLC patients with PD-L1 TPS≥50% (n=10).

2. Combination Therapies Demonstrate Favorable Tolerability and Promising Efficacy
Safety data from multiple cohorts of CS2009 combined with standard chemotherapy showed that the combinations were well-tolerated across tumor types, with CS2009 without increasing the incidence or severity of chemotherapy-related adverse events. Initial potent antitumor activity was observed with combination treatment in first-line NSCLC and first-line CRC.

Efficient and Clearly-Defined Global Development Strategy

CStone plans to initiate the first set of Phase III global MRCTs for CS2009 by the end of 2026, focusing on indications including NSCLC, CRC, and SCLC.

Additional Phase I and Phase II clinical data for CS2009 are expected to be presented at the 2026 ASCO and/or ESMO Annual Meetings.

About CS2009 (PD-1/VEGF/CTLA-4 Trispecific Antibody)

CS2009, an innovative trispecific antibody designed and developed by CStone, with the potential to be first- or best-in-class. It combines three clinically validated targets—PD-1, VEGFA, and CTLA-4—and exerts multidimensional antitumor effects through synergistic actions. Specifically, anti-PD-1 activity reverses T cell exhaustion, anti-CTLA-4 activity promotes T cell activation and proliferation, while anti-VEGFA activity blocks tumor angiogenesis and improves the tumor micro-environment (TME). In the TME, anti-PD-1 and anti-CTLA-4 activities are significantly enhanced by crosslinking with VEGFA. Meanwhile, CS2009 preferentially blocks PD-1 and CTLA-4 on double-positive tumor-infiltrating T cells while minimizing interference with CTLA-4 regulation in peripheral T cells.

About CStone Pharmaceuticals

CStone (HKEX: 2616), established in late 2015, is an innovation-driven biopharmaceutical company focused on the research and development of therapies for oncology, immunology, inflammation, and other key disease areas. Dedicated to addressing patients' unmet medical needs in China and globally, the Company has made significant strides since its inception. To date, the Company has successfully launched 4 innovative drugs and secured approvals for 21 new drug applications covering 9 indications. The company's pipeline is balanced by 16 promising candidates, featuring antibody-drug conjugates (ADCs), multispecific antibodies, immunotherapies and precision medicines. CStone also prides itself on a management team with comprehensive experiences and capabilities that span the entire drug development spectrum, from preclinical and translational research to clinical development, drug manufacturing, business development, and commercialization. For more information about CStone, please visit: www.cstonepharma.com.

SOURCE CStone Pharmaceuticals