On February 24, 2025 CStone Pharmaceuticals ("CStone", HKEX: 2616), an innovation-driven biopharmaceutical company focused on the research and development of anti-cancer therapies, reported the publication of the GEMSTONE-303 study results for sugemalimab (brand name: Cejemly) in the prestigious Journal of the American Medical Association (JAMA) (Press release, CStone Pharmaceauticals, FEB 24, 2025, View Source [SID1234650487]).

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GEMSTONE-303 is a Phase 3, randomized, double-blind, placebo-controlled study designed to evaluate the efficacy of sugemalimab in combination with capecitabine and oxaliplatin (CAPOX) compared to placebo plus CAPOX as first-line treatment for patients with unresectable locally advanced or metastatic G/GEJ adenocarcinoma with PD-L1 CPS ≥5. The dual primary endpoints were OS and investigator-assessed PFS. Key secondary endpoints included PFS assessed by the Blinded Independent Central Review Committee (BICR), objective response rate (ORR), and duration of response (DoR).

The GEMSTONE-303 article published in JAMA highlights the following key efficacy and safety findings:

In patients with PD-L1 CPS ≥5, the sugemalimab group showed statistically significant and clinically meaningful improvements in both OS and PFS compared with the control group.
Median OS was 15.6 months in the sugemalimab group compared with 12.6 months in the control group, with a hazard ratio (HR) of 0.75 (95% CI, 0.61-0.92), P=0.006, indicating that sugemalimab plus CAPOX could reduce the risk of death by 25%.
Median PFS was 7.6 months in the sugemalimab group versus 6.1 months in the control group, with a HR of 0.66 (95% CI, 0.54-0.81), P<0.001.
Grade ≥3 treatment-related adverse events (TRAE) occurred in 53.9% of patients in the sugemalimab group and 50.6% in the control group, indicating that the safety of this combination regimen was manageable.
Subgroup analyses demonstrated consistent clinical benefits across all pre-defined subgroups, including patients with varying PD-L1 expression levels:

Sugemalimab plus CAPOX significantly prolonged OS in patients with PD-L1 CPS ≥10; median OS was 17.8 months in the sugemalimab group compared with 12.5 months in the control group, with a HR of 0.64 (95% CI, 0.48-0.85), P=0.002.
In patients with PD-L1 CPS ≥10, median PFS was 7.8 months in the sugemalimab group compared with 5.5 months in the control group, with a HR of 0.58 (95% CI, 0.43-0.77), P<0.001.
In patients with PD-L1 CPS ≥10, ORR was 71.4% in the sugemalimab group compared with 48.6% in the control group.
Dr. Jason Yang, CEO, President of R&D, and Executive Director at CStone, stated: "We are honored to see the GEMSTONE-303 study results published in JAMA. This study establishes sugemalimab in combination with chemotherapy as the new standard first-line treatment for patients with PD-L1 CPS ≥5 G/GEJ adenocarcinoma. To date, sugemalimab has been approved for five indications in China. Internationally, we have expanded its regulatory pathways and forged commercialization partnerships in various global markets. The compelling clinical data from GEMSTONE-303 reinforce our confidence in advancing the global registration and commercialization of sugemalimab. We are committed to unlocking its full clinical potential and providing greater survival benefits to patients worldwide."

Professor Lin Shen, Peking University Cancer Hospital, the leading principal investigator of the GEMSTONE-303 study, said: "Before the availability of PD-1 monoclonal antibodies, chemotherapy was the standard first-line treatment for unresectable, locally advanced or metastatic G/GEJ adenocarcinoma, with median OS rarely exceeding one year. The combination of anti-PD-1 antibodies and chemotherapy has significantly extended survival for these patients. The GEMSTONE-303 study builds on this progress. As the first anti-PD-L1 antibody approved for this patient population, sugemalimab specifically targeted the PD-L1-expressing population in its pivotal study, achieving significant efficacy with a manageable safety profile. The acceptance and publication of these results in JAMA affirm the innovation of GEMSTONE-303 and the valuable contributions of all researchers and participants involved."

About Sugemalimab

The anti-PD-L1 monoclonal antibody sugemalimab was developed by CStone using OmniRat transgenic animal platform, which allows creation of fully human antibodies in one step. Sugemalimab is a fully human, full-length anti-PD-L1 immunoglobulin G4 (IgG4) monoclonal antibody, which may reduce the risk of immunogenicity and toxicity for patients, a unique advantage over similar drugs.

The National Medical Products Administration (NMPA) of China has approved sugemalimab for five indications:

In combination with chemotherapy as first-line treatment of patients with metastatic squamous and non-squamous NSCLC;
For the treatment of patients with unresectable Stage III NSCLC whose disease has not progressed following concurrent or sequential platinum-based chemoradiotherapy;
For the treatment of patients with relapsed or refractory extranodal NK/T-cell lymphoma;
In combination with fluorouracil and platinum-based chemotherapy as first-line treatment of patients with unresectable locally advanced, recurrent or metastatic ESCC; and
In combination with fluoropyrimidine- and platinum-containing chemotherapy as first-line treatment for unresectable locally advanced or metastatic gastric or gastroesophageal junction (G/GEJ) adenocarcinoma with a PD-L1 expression CPS ≥5.
The European Commission (EC) has approved sugemalimab (brand name: Cejemly) in combination with platinum-based chemotherapy for the first-line treatment of patients with metastatic NSCLC with no sensitizing EGFR mutations, or ALK, ROS1 or RET genomic tumor aberrations.

The Medicines and Healthcare products Regulatory Agency (MHRA) in the United Kingdom has approved the marketing authorization application for sugemalimab in combination with platinum-based chemotherapy for first-line treatment of metastatic NSCLC with no sensitizing EGFR mutations, or ALK, ROS1 or RET genomic tumor aberrations.