For two reasons, MSI-GC classification is clinically relevant: (1) MSI-GCs predict improved patient outcomes (Mathiak et al. 2017; Pietrantonio et al. 2019; Guan et al. 2021); (2) MSI-GCs frequently express immune checkpoint molecules such as PD-L1 (Fig. 1) making them eligible for treatment with immune checkpoint inhibitors (Cancer Genome Atlas Research 2014; Böger et al. 2016; Pietrantonio et al. 2021). This evidence concerns the gene CD274 and gastric cancer.