Star Metro - CS2009 (PD-1/VEGF/CTLA-4 Trispecific Antibody) ASCO 2026 Key Highlights

I. Trispecific Design Rationale and Differentiated Advantages

1. Greater Potential for Long-Term Survival Benefit vs. PD-1+VEGF Combinations, with Low CTLA-4-Related Toxicity and Favorable Tolerability

CS2009 was designed to restore T-cell effector function, remodel the tumor microenvironment (TME), and enhance T-cell priming via simultaneous targeting of PD-1, VEGF, and CTLA-4, aiming to generate deeper and more durable anti-tumor immune responses.

• Differentiated CTLA-4 Design: The CTLA-4 component is engineered to avoid excessive activation of peripheral CTLA-4 single-positive T cells, thereby reducing systemic immune toxicity. Combined with VEGF-mediated tumor enrichment, this design preserves the immune-stimulatory benefit of CTLA-4 blockade while substantially improving tolerability. Clinical data has demonstrated that CTLA-4-related toxicities with CS2009 are notably lower than that of conventional CTLA-4 antibody regimens, with immune-related adverse events (irAEs) approaching incidence typically seen with PD-1 monotherapy or PD-1-based bispecific antibodies.

• Advantage of Continuous Dosing: Unlike conventional CTLA-4 antibodies, which are often limited to two or three doses due to tolerability concerns, CS2009 can be administered continuously, therefore fully leveraging the CTLA-4 mechanism-not only initiating and enhancing existing anti-tumor T-cell responses but also continuously priming new T-cell clones against newly released tumor antigens throughout treatment. This ongoing expansion of the anti-tumor T-cell repertoire, combined with CS2009's favorable tolerability, is expected to drive more durable immune responses, prolong clinical benefit, and ultimately improve overall survival.

• Pharmacodynamic Validation: Dose-dependent upregulation in ICOS, a recognized pharmacodynamic marker of CTLA-4 pathway activation and T-cell activation, were observed. The ICOS elevation suggests that CS2009 continuously promotes T-cell priming and clonal expansion, validating the biological activity of its CTLA-4 module and providing biological basis for long-term anti-tumor activity.

Industry challenge: Historically, most anti-VEGF plus PD-(L)1 regimens have primarily improved progression-free survival (PFS), while overall survival (OS) benefits remains highly uncertain. By incorporating a CTLA-4 mechanism, CS2009 aims to break through this limitation.

2. Low VEGF-Related Toxicity Supporting More Adequate Treatment Exposure and Sustained Clinical Benefit

Pharmacodynamic data demonstrated:

• Circulating VEGF levels have declined continuously following dosing, and no clear rebound has been observed after up to 147 days of follow-up.

This pattern differs from results reported with traditional anti-VEGF antibodies or PD-1/VEGF bispecifics, potentially due to CS2009's enrichment in the tumor microenvironment and CTLA-4-mediated internalization and clearance of VEGF-antibody complexes. This may reduce reflux of VEGF and its antibody-bound complexes into the peripheral circulation, thereby lowering VEGF-related systemic toxicities such as hypertension and proteinuria.

Clinical data demonstrated:

• The incidence of Grade ≥3 VEGF-related treatment-related adverse events (TRAEs) is only 5.1%, notably lower than reported rates for certain VEGF-based bispecifics.

Industry challenge: VEGF is both a critical efficacy driver and a major source of toxicity in combination therapies. Achieving an optimal balance between efficacy and tolerability, particularly in elderly and high-risk patients, remains a longstanding, unresolved challenge in the VEGF field.

3. Consistent Activity Observed Across Multiple "Cold" Tumors, Highlighting the Value of the CTLA-4 Module and the Trispecific Mechanism

Promising anti-tumor activity has been observed in several traditionally immunotherapy-insensitive tumor types, including: Immunotherapy-resistant non-small cell lung cancer (NSCLC), pMMR/MSS metastatic colorectal cancer (mCRC), Soft tissue sarcoma (STS), Non-clear cell renal cell carcinoma (nccRCC).

These findings suggest that the combined blockade of PD-1 and CTLA-4, together with VEGF modulation, may enhance T-cell priming, broaden T-cell clonal diversity, promote durable immune memory, and improve T-cell infiltration within the TME-extending immune responsiveness to tumors that were previously I/O-insensitive. The consistent efficacy signals across multiple cold tumors support the ability of CS2009's PD-1, CTLA-4 and VEGF synergism to reshape the immunosuppressive TME, expand the I/O-benefiting population, and demonstrate the potential to transcend the efficacy boundaries of traditional PD-1 inhibitors and PD-1/VEGF bispecifics.

Industry challenge: Effective immunotherapy options remain limited for cold tumors. PD-1 plus CTLA-4 blockade is still one of the most widely recognized strategies for enhancing immunotherapy responsiveness.

4. Consistent Benefit Observed Across Squamous and Non-Squamous NSCLC

• Across multiple NSCLC treatment settings, comparable response rates were observed in both squamous and non-squamous patients.

CS2009 is showing a trend of consistent benefit across histological subtypes, indicating that its mechanism may not depend on a particular pathologic type and may cover a broader population of NSCLC patients, enhancing the probability of success in future global registrational trials.

Industry challenge: Notable differences in efficacy between squamous and non-squamous NSCLC often limit the label expansion and commercial potential of certain products.

II. Favorable Safety Profile with Notably Lower VEGF-Related Toxicity Compared with Bispecifics

Safety data from the ongoing Phase I study in a mixed tumor population (N=118):

• Grade ≥3 TRAE incidence: 24.6%;

• Grade ≥3 irAE incidence: 12.7%;

• Grade ≥3 VEGF-related TRAE incidence: 5.1%.

Focusing on the later-line NSCLC cohort (n=57):

• Grade ≥3 TRAE rate: 19.3%;

• Grade ≥3 irAE rate: 12.3%;

• VEGF-related Grade ≥3 TRAE rate: 5.3%;

• Consistent with the safety profile of the overall heavily pretreated mixed-tumor population.

Overall:

• CTLA-4-related toxicity appears very well controlled.

• No new or unexpected safety signals have been identified.

• The overall safety profile is comparable to that of PD-1/VEGF bispecific antibodies, while VEGF-related toxicity appears substantially lower.

This safety profile provides an important foundation for long-term dosing and future global registrational development.

III. Efficacy in "Cold" Tumors Demonstrates Differentiated Clinical Value

CS2009 has demonstrated meaningful clinical activity across multiple "cold" tumors, highlighting the differentiated mechanism.

1. Monotherapy in Later-Line pMMR/MSS mCRC

• All enrolled patients had heavily pretreated, refractory CRC, including cases with BRAF mutations and right-sided tumors.

• CS2009 monotherapy achieved an ORR of 25% and a DCR of 87.5%.

Given that ORR in later-line colorectal cancer are typically in the single digits, these results demonstrate clinically meaningful anti-tumor activity.

More importantly, efficacy signals emerging in a typical cold-tumor population further supports the differentiated value of the CTLA-4 module.

2. Combination with XELOX in First-Line pMMR/MSS mCRC

• The study did not select patients by tumor sidedness, molecular subtype, or liver metastasis; the enrolled population better reflects real-world clinical practice.

• To date, all six patients have experienced tumor shrinkage, and three patients achieved a partial response (PR) at their first efficacy assessment.

• ORR was 66.7%, and DCR was 100%.

Although the sample size remains small, highly consistent early efficacy signals have already been observed, providing positive support for subsequent global registrational development.

The Company plans to expand the cohort to approximately 40 patients to generate a more comprehensive proof-of-concept (POC) dataset for upcoming discussions with the global regulatory authorities including the U.S. Food and Drug Administration (FDA) and China's National Medical Products Administration (NMPA) on a Phase III global registrational clinical trial.

3. Other "Cold" Tumors

• Monotherapy in Later-line Soft Tissue Sarcoma (STS): ORR 33.3%, DCR 66.7%;

• Monotherapy in Later-line non-clear cell renal cell carcinoma (nccRCC): ORR 33.3%, DCR 100%;.

• Durable responses have also been observed. Notably, the first patient enrolled in Phase I (an Australian female) has experienced sustained tumor shrinkage of more than 40% over 12 months.

IV. NSCLC: Multi-Dimensional Data Support Global Registrational Development

Dimension 1: Later-Line NSCLC Monotherapy (Pretreated with IO, Chemotherapy, ADCs, or Bispecifics)

• Overall ORR in the 30 mg/kg cohort: 24% (squamous 25%, non-squamous 23.1%, consistent benefit); DCR 60%;

• In second-line NSCLC (30 mg/kg, post IO + chemotherapy): ORR improved to 30.8%, DCR 84.6%.

• In such post-PD-(L)1 patient populations, standard-of-care ORRs are generally low, thus CS2009 has demonstrated competitive single-agent activity.

Additional observations include:

• 6-month duration-of-response (DOR) rate exceeded 80% (i.e., more than 80% of responders remained in response at 6 months);

• Depth of response has continued to deepen over time;

• DOR data are still maturing.

Dimension 2: Later-Line NSCLC in Combination with Docetaxel

• All six evaluable patients experienced tumor shrinkage, resulting in an ORR of 66.7% and a DCR of 100%.

Although the sample size is currently small, these results are already very competitive within this class of studies.

The company plans to expand the cohort to approximately 20 patients to inform subsequent registrational decisions.

Dimension 3: First-Line NSCLC Monotherapy (PD-L1 TPS ≥50%)

• Among 16 patients, ORR was 81.3% and DCR was 100%;

• Squamous ORR 87.5%, non-squamous ORR 75%, consistent benefit;

• Earlier data (March 2026) showed 9 PRs out of 10 patients; among the 6 newly enrolled patients, 4 achieved a PR at their first tumor assessment, bringing the total number of PRs observed to 13;

• No responding patients have experienced rapid disease progression, and patients have shown deepening responses over time.

While cross-trial comparisons have limitations, CS2009's single-agent ORR in first-line NSCLC (PD-L1 TPS ≥50%) has reached a best-in-class range among comparable studies globally, demonstrating highly competitive clinical potential.

Note: Data in the PD-L1 1%-49% population continue to mature.

Dimension 4: First-Line NSCLC in Combination with Chemotherapy (Squamous, PD-L1 Low or Negative)

• Among 8 squamous patients enrolled to date, 7 patients have PD-L1 ≤1% (low/negative), and 1 patient has PD-L1 ≤5% (low expression); median age is 70 years;

• ORR was 75% and DCR was 100%; among PD-L1-negative patients, ORR reached 100%;

Particularly noteworthy:

• A 100% response rate was observed among PD-L1-negative patients;

• Encouraging efficacy was also observed in elderly patients.

Although longer follow-up is required, positive and consistent early efficacy signals are evident.

Note: Enrollment is ongoing in the first-line all-comer squamous NSCLC (Chemo Combo) and first-line non-squamous NSCLC (Chemo Combo) cohorts. Data will be disclosed subsequently.

V. Global Registration Strategy

CS2009 is advancing through a global multi-regional clinical development pathway.

• Rapid enrollment supports timely data package generation and regulatory engagement.

• Registrational studies will not be conducted in a single country; all key registrational studies will be global multi-regional clinical trials (MRCTs) using current international standard-of-care comparators (pembrolizumab / pembrolizumab + chemotherapy / bevacizumab + chemotherapy). The trial designs and timelines are independent of data readouts from other bispecific/trispecific competitors, giving CS2009 a self-determined development advantage.

  • October 2026: Discuss the Phase III global registrational clinical trial protocol for first-line NSCLC + chemotherapy (vs. pembrolizumab + chemotherapy) .

  • Q4 2026: Discuss the Phase III global registrational clinical trial protocol for first-line mCRC + chemotherapy (vs. bevacizumab + chemotherapy) .

  • Early 2027: Discuss the Phase III global registrational clinical trial protocol forsecond-line NSCLC (CS2009 + docetaxel vs. docetaxel) and first-line NSCLC monotherapy (head-to-head vs. pembrolizumab) .

20-60 patients of POC data are expected per indication. The company has already established a clinical, CMC (Chemistry, Manufacturing and Controls) and operational system that supports global development, laying the groundwork for subsequent global multi-center Phase III MRCTs .

VI. Key Catalysts in 2026

• Late August 2026: Interim results update featuring more mature post-ASCO clinical data.

• Around October 2026: FDA discussion regarding the Phase III global registrational clinical trial protocol for first-line NSCLC + chemotherapy.

• Q4 2026: FDA discussion regarding Phase III global registrational clinical trial protocol for first-line CRC + chemotherapy.

• Q4 2026: ESMO Congress - clinical data updates for CRC, NSCLC, and other indications.

• End of 2026: Initiation of the first-wave global Phase III MRCTs.

Importantly, all pivotal studies are benchmarked against current global standard-of-care comparators, without dependency on competitors' development progress.

VII. Business Development Progress

In-depth discussions are ongoing with multiple multinational pharmaceutical companies (MNCs). Key areas of partner interest include: trispecific antibody design rationale, safety profile, clinical data in NSCLC and CRC, global registration strategy.

As data continue to mature and the global development advances, the differentiated value of CS2009 is gaining increasingly broad and strong recognition.

VIII. Management Confidence and Capital Markets Initiatives

1. Share Purchases by Management and the Board:

Management and the Board believe that the recent share price volatility has significantly deviated from the Company's fundamental progress. Management and Board members have expressed their confidence in the long-term value of CS2009 and the Company's growth prospects by increasing their shareholdings.

2. Anticipated inclusion in the Hong Kong Stock Connect Scheme

Management expressed a positive expectation that the Company will be included in the Stock Connect scheme at the September 2026 adjustment window.

IX. Key Takeaway

The ASCO 2026 data mark CS2009's transition from mechanism validation to the clinical proof-of-concept (POC) stage. Its differentiated trispecific design not only delivers an excellent safety profile, but also consistently generates clinically meaningful efficacy signals and durable responses across a range of traditional I/O-cold tumors and lung cancer populations. As the key CRC and NSCLC programs move toward global registrational development, CS2009 is steadily emerging as a next-generation I/O backbone agent with significant potential.

About CStone

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.

IR contact: [email protected]

PR contact: [email protected]

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SOURCE: CStone Pharmaceuticals

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P.Beaulieu--SMC