Pietrantonio F, Miceli R, Raimondi A, et al. - Among patients with resectable gastric cancer (GC) participating in the MAGIC, CLASSIC, ARTIST, and ITACA-S trials, researchers determined the prognostic/predictive role of microsatellite instability (MSI) via this multinational, individual-patient-data meta-analysis. Multivariable Cox models (MVM) were used to perform prognostic analyses. The estimated 5-year disease-free survival (DFS) was 71.8% vs 52.3% and the 5-year overall survival (OS) was 77.5% vs 59.3% in MSI-high vs MSI-low/microsatellite stable (MSS) comparisons. The link of MSI as well as pT, pN, ethnicity, and treatment, with longer DFS and OS was revealed in MVM. A benefit of chemotherapy plus surgery was evident in patients with MSI-low/MSS GC but not in those with MSI-high GC. MSI was identified as a robust prognostic marker in patients with resectable primary GC and, was recommended to be used as a stratification factor by clinical trials. A prospective inquiry for chemotherapy omission and/or immune checkpoint blockade was recommended in MSI-high GCs according to clinically and pathologically defined risk of relapse.