Tislelizumab Plus Chemotherapy as First-line Treatment for Advanced Esophageal Squamous Cell Carcinoma and Gastric/Gastroesophageal Junction Adenocarcinoma

Purpose: This phase II study (NCT03469557) assessed safety/tolerability and antitumor activity of first-line tislelizumab, a monoclonal antibody against programmed cell death-1, plus chemotherapy in patients with locally advanced/metastatic esophageal squamous cell carcinoma (ESCC) or gastric/gastroesophageal junction (G/GEJ) adenocarcinoma. Patients and Methods: Patients with ESCC received tislelizumab [200 mg i.v. every 3 weeks (Q3W)] plus cisplatin (80 mg/m(2) i.v. Q3W for <= 6 cycles) and fluorouracil (800 mg/m(2)/day i.v., Days 1-5 Q3W for <= 6 cycles); patients with G/GEJ adenocarcinoma received tislelizumab (200 mg i.v. Q3W) plus oxaliplatin (130 mg/m(2) i.v. Q3W for up to six cycles) and oral capecitabine (1,000 mg/m(2) twice daily, Days 1-14 Q3W). The safety/tolerability profile of combination therapy was the primary endpoint; secondary endpoints included objective response rate (ORR), duration of response (DoR), disease control rate (DCR), and progression-free survival per RECIST v1.1. Exploratory endpoints included overall survival and potential predictive biomarkers. Results: As of March 31, 2019, 30 patients (n = 15 per cohort) were enrolled. Most common adverse events considered related to tislelizumab and/or chemotherapy were anemia (n = 18), decreased appetite (n = 17), nausea (n = 16), and asthenia (n = 15). One patient experienced fatal hepatic dysfunction, confounded by progressive disease and underlying hepatitis, attributed to treatment by the investigator. Confirmed ORRs and DCRs were 46.7% and 80%, respectively, for both ESCC and G/GEJ adenocarcinoma. In ESCC, median DoR was 12.8 months (95% confidence interval, 3.5-12.8); DoR was not yet mature for the G/GEJ cohort. Conclusions: Tislelizumab plus chemotherapy demonstrated durable responses with manageable tolerability in patients with advanced ESCC or G/GEJ adenocarcinoma.