BACKGROUND: In resectable gastric/gastroesophageal junction adenocarcinoma, microsatellite instability-high (MSI-H) confers improved survival, but limited benefit from chemotherapy. Immunotherapy may eliminate the need for chemotherapy or surgery. PATIENTS AND METHODS: INFINITY is a multicenter, multicohort phase II trial (NCT04817826) investigating in cohort 1 the activity and safety of tremelimumab + durvalumab (T300/D) as neoadjuvant treatment of mismatch repair deficient/MSI-H, resectable gastric/gastroesophageal junction adenocarcinoma. Primary endpoint was pathologic complete response (pCR) rate
Secondary endpoints: progression-free survival (PFS), overall survival (OS), quality of life, and translational analyses. In cohort 2, the activity and safety of T300/D was explored as definitive treatment in patients achieving clinical complete response (cCR). Primary endpoint was 2-year cCR rate, and secondary endpoints were PFS, OS, quality of life, gastrectomy-free survival and translational analyses. RESULTS: In cohort 1, 18 patients were recruited and 15 evaluable. pCR and major pathologic response-pCR were 60% and 80%, respectively. Since pCR rate in T4 tumors was 17%, this subgroup of patients was excluded from enrollment in cohort 2. At 28.1 months median follow-up, 24-month gastric cancer-specific PFS and OS rates were 85% and 92%, respectively. In cohort 2, 18 patients were enrolled and 17 assessable, and 13 had cCR and started non-operative management. At 11.5 months median follow-up, one patient had local regrowth and underwent salvage surgery
12-month gastrectomy-free survival was 64.2%. CONCLUSIONS: The INFINITY study provided promising activity results of a chemo-free T300/D combination regimen as preoperative treatment in mismatch repair deficient/MSI gastric/gastroesophageal junction adenocarcinoma and the first available feasibility results of a non-operative management strategy in this disease setting, worthy of further validation in larger cohorts.