Tislelizumab plus chemotherapy versus placebo plus chemotherapy as first line treatment for advanced gastric or gastro-oesophageal junction adenocarcinoma: RATIONALE-305 randomised, double blind, phase 3 trial

OBJECTIVE: To evaluate the efficacy and safety of tislelizumab added to chemotherapy as first line (primary) treatment for advanced gastric or gastro-oesophageal junction adenocarcinoma compared with placebo plus chemotherapy. DESIGN: Randomised, double blind, placebo controlled, phase 3 study. SETTING: 146 medical centres across Asia, Europe, and North America, between 13 December 2018 and 28 February 2023. PARTICIPANTS: 1657 patients aged ≥18 years with human epidermal growth factor receptor 2 negative locally advanced unresectable or metastatic gastric or gastro-oesophageal junction adenocarcinoma, regardless of programmed death-ligand 1 (PD-L1) expression status, who had not received systemic anticancer therapy for advanced disease. INTERVENTIONS: Patients were randomly (1:1) assigned to receive either tislelizumab 200 mg or placebo intravenously every three weeks in combination with chemotherapy (investigator's choice of oxaliplatin and capecitabine, or cisplatin and 5-fluorouracil) and stratified by region, PD-L1 expression, presence or absence of peritoneal metastases, and investigator's choice of chemotherapy. Treatment continued until disease progression or unacceptable toxicity. MAIN OUTCOME MEASURES: The primary endpoint was overall survival, both in patients with a PD-L1 tumour area positivity (TAP) score of ≥5% and in all randomised patients. Safety was assessed in all those who received at least one dose of study treatment. RESULTS: 12.9 months; hazard ratio 0.80 (0.70 to 0.92); P=0.001 (final analysis)). Grade 3 or worse treatment related adverse events were observed in 54% (268/498) of patients in the tislelizumab plus chemotherapy arm versus 50% (246/494) in the placebo plus chemotherapy arm. CONCLUSIONS: Tislelizumab added to chemotherapy as primary treatment for advanced or metastatic gastric or gastro-oesophageal junction adenocarcinoma provided superior overall survival with a manageable safety profile versus placebo plus chemotherapy in patients with a PD-L1 TAP score of ≥5%, and in all randomised patients. TRIAL REGISTRATION: ClinicalTrials.gov NCT03777657.