A Phase II Study of Ipilimumab N01 Plus Sintilimab for MSI-H or dMMR Gastric and Gastroesophageal Junction Cancer

This is a prospective, multicenter phase II clinical study designed to evaluate the efficacy and safety of ipilimumab N01 in combination with sintilimab in patients with MSI-H/dMMR gastric or gastroesophageal junction adenocarcinoma. The study comprises two cohorts. Cohort 1 plans to enroll 19 treatment-naïve patients with resectable locally advanced (cT2-4N+M0) MSI-H/dMMR gastric or gastroesophageal junction adenocarcinoma as determined by imaging (contrast-enhanced CT or contrast-enhanced MRI), who will receive 4 cycles of neoadjuvant therapy with ipilimumab N01 (1 mg/kg IV, Q6W, D1, for a total of 2 doses) in combination with sintilimab (200 mg IV, Q3W, D1) (21 days per cycle), followed by radical D2 resection, and then 13 cycles of adjuvant sintilimab monotherapy postoperatively. Cohort 2 plans to enroll 17 patients with initially unresectable MSI-H/dMMR gastric or gastroesophageal junction adenocarcinoma, who will receive conversion therapy with sintilimab in combination with ipilimumab N01, with MDT assessment of surgical feasibility every 2 cycles; those deemed operable will undergo surgical resection followed by adjuvant sintilimab monotherapy for up to 1 year postoperatively, while those deemed inoperable will continue treatment until PD or intolerable toxicity.