Zanidatamab with and without Tislelizumab in HER2-Positive Gastroesophageal Cancer

BACKGROUND: Zanidatamab, a dual human epidermal growth factor receptor 2 (HER2)-targeted bispecific antibody, plus chemotherapy both with and without tislelizumab (anti-programmed death 1), showed encouraging efficacy and safety as first-line therapy in phase 2 studies involving patients with HER2-positive gastroesophageal adenocarcinoma. METHODS: In an open-label, phase 3 trial, we randomly assigned, in a 1:1:1 ratio, patients with previously untreated, centrally confirmed HER2-positive advanced gastroesophageal adenocarcinoma to receive zanidatamab and tislelizumab plus chemotherapy, zanidatamab plus chemotherapy, or trastuzumab plus chemotherapy. The two primary end points were progression-free survival and overall survival. RESULTS: At a median follow-up of 25.9 months, progression-free survival was longer with zanidatamab-tislelizumab-chemotherapy (median among 302 patients, 12.4 months) and zanidatamab-chemotherapy (median among 304 patients, 12.4 months) than with trastuzumab-chemotherapy (median among 308 patients, 8.1 months) (hazard ratio for progression or death with zanidatamab-tislelizumab-chemotherapy, 0.63 [95% confidence interval {CI}, 0.51 to 0.78]; hazard ratio with zanidatamab-chemotherapy, 0.65 [95% CI, 0.52 to 0.81]; P