In a 2021 meta-analysis of 2545 patients with GC with assessable MSI status data, Pietrantonio et al. found that the HR for OS with anti-PD-1-based regimens was 0.34 (95% CI, 0.21–0.54) compared with 0.85 (95% CI, 0.71–1.00) for MSS cancers, as well as that the treatment effect significantly differed between the two subgroups (P for interaction = 0.003) [65]. This evidence concerns the gene PDCD1 and gastric cancer.