Purpose:The benefit of chemotherapy in locally advanced gastroesophageal cancer with deficient mismatch repair (dMMR) or microsatellite instability-high (MSI-H) remains uncertain.This study aimed to identify optimal postoperative management strategies for dMMR/MSI-H gastric or gastroesophageal junction (EGJ) adenocarcinoma.Materials and Methods: Patients with pathologically confirmed stage II-IVA dMMR/ MSI-H gastric or EGJ adenocarcinoma who underwent D2 gastrectomy between 2015 and 2022 were retrospectively enrolled from 4 centers.Postoperative management strategies included observation, chemotherapy, immune checkpoint inhibitors (ICIs), or ICIs combined with chemotherapy (ICI-chemo).The primary endpoint was 2-year event-free survival (EFS), and the secondary endpoints were EFS and overall survival (OS).Results: A total of 156 patients were included in the analysis.The highest 2-year EFS was observed in the ICI-chemo group (87.5%), followed by the observation group (86.7%) and the ICI monotherapy group (86.5%), whereas chemotherapy alone yielded the lowest rate (75.7%).Patients with earlier-stage disease had significantly lower risks of progression (hazard ratio HR, 0.29; 95% confidence interval CI, 0.16-0.53)and death (HR, 0.30; 95% CI, 0.14-0.64).EFS improved progressively from chemotherapy to observation and further to ICI-containing regimens across stages.In stage III-IVA disease, ICI monotherapy
Hua et al. (2026) studied this question.