Background: A large proportion of patients (pts) with gastric cancer present with locally advanced or metastatic disease, which is linked with poor survival. Platinum- and fluoropyrimidine-based doublet chemotherapy (CTx) remains the standard of care in advanced gastric cancers. Based on recent clinical data, immuno-oncology (IO) agents plus CTx can improve overall survival (OS) in pts with locally advanced unresectable or metastatic gastric or gastroesophageal junction (GEJ) adenocarcinoma who have human epidermal growth factor receptor 2 negative/low expression (HER2–) and have not been previously treated for advanced/metastatic disease. GEMINI-Gastric (NCT05702229) is a phase 2, open-label, multidrug, multicenter, master protocol study designed to assess the efficacy, safety, tolerability, pharmacokinetics (PK), and immunogenicity of multiple novel IO + CTx combination therapies in this setting. Methods: Adults (≥18 years) with previously untreated HER2– locally advanced unresectable, or metastatic gastric or GEJ adenocarcinoma are eligible. Pts should have measurable target disease per RECIST v1.1 and an ECOG performance status of 0–1. The GEMINI-Gastric design allows assessment of multiple novel agents plus CTx in different substudies (Table). Novel agents include: volrustomig, an anti-PD-1/CTLA-4 bispecific humanized IgG1 monoclonal antibody (mAb); rilvegostomig, an anti-PD-1/TIGIT bispecific humanized IgG1 mAb; AZD0901, a claudin18.2-targeted antibody-drug conjugate; and AZD7789, an anti-PD-1/TIM-3 bispecific mAb. Co-primary endpoints are objective response rate and progression-free survival (PFS) at 6 months by investigator assessment per RECIST v1.1. Secondary endpoints include safety, duration of response, PFS, OS, PK, and immunogenicity. Sample sizes have been selected to provide adequate precision for the primary endpoints. The study is currently recruiting at sites in the US, Europe, and Asia. Clinical trial information: NCT05702229.

5-FU, 5-fluorouracil; CLDN18.2+, claudin18.2 positive; FOLFOX, 5-FU, oxaliplatin, and leucovorin; HER2–, human epidermal growth factor receptor 2 negative; Pts, patients; XELOX, capecitabine and oxaliplatin.