This phase II study evaluates dostarlimab followed by a watch-and-wait strategy in patients with localized dMMR/MSI-H gastric or gastroesophageal junction (GEJ) adenocarcinoma. The study aims to determine whether surgery can be safely avoided in patients achieving a complete response, defined by negative endoscopy and tumor-free biopsies after treatment.
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Is capable of giving signed and dated informed consent,
Has an ECOG PS of 0-1,
A patient over 70 years of age is eligible to participate in the main initial cohort if the patient respects all the criteria and has a score G8 of ≥14.
A patient over 70 years with a score G8 <14 should have a consultation with an onco-geriatrician to determine the best treatment or therapeutic strategy based on age and co-morbidity. After this consultation, the patient is eligible for main initial cohort if "fits for surgery" with no contraindications to repeated UGI endoscopy with biopsies (no change to the initial protocol) and can follow the study plan and procedures outlined in the study.