Immunotherapy using immune checkpoint blockades (ICBs), such as programmed cell death protein 1 (PD-1) or programmed death-ligand 1 (PD-L1) inhibitors, has achieved great success in treating various types of cancers, and MSI-H has been established as a tissue-agnostic predictive biomarker for the therapeutic response to anti-PD-1/PD-L1 ICBs [13, 14]. This evidence concerns the gene PDCD1 and cancer.