Di Bartolomeo M, Morano F, Raimondi A, et al. - In view of the observed improved survival and no benefit or harm from adjuvant and/or perioperative chemotherapy among patients with high microsatellite instability (MSI) gastric cancer (GC), researchers sought to determine the role of the immune microenvironment in GC. From patients recruited in ITACA-S, a randomized adjuvant trial of 5-FU/LV vs sequential FOLFIRI and cisplatin-docetaxel, they obtained 256 tumor tissue blocks for the present study. The analysis revealed MSI-high tumors in 9% of the patients, a high inflammatory reaction in 23%, tumor programmed death-ligand 1 (PD-L1) ≥ 1% in 11%, and stromal PD-L1 ≥ 1% in 11%. Multivariable analysis revealed an independent association of only MSI with both disease-free survival (DFS) and overall survival (OS), however, the inflammatory reaction had an independent association only with OS. They noted a significantly longer DFS for patients with tumor PD-L1 ≥ 1% in sequential chemotherapy than in the 5-FU/LV arm and a trend for OS. Data thereby indicate the possible utility of MSI status as a prognostic biomarker in patients with radically resected stage II–III GC and as stratification factor in future trials.