Immunohistochemistry showed a mean CD8+ tumor-infiltrating lymphocyte density of 59.5 ± 14.3 cells per high-power field, a programmed death-ligand 1 (PD-L1) combined positive score (CPS) of ≥ 70% (clone 28-8), and a germline TP53 p.R106C mutation.<h4>Conclusion</h4>This case illustrates that even in MSS gastric cancer with low TMB levels, exceptionally high PD-L1 expression may predict a profound response to ICI-based therapy. Here, TP53 is linked to gastric cancer.