PDCD1 and melanoma: Immune checkpoint inhibitors (ICIs) that target PDCD1/CD274(PD-1/PD-L1) have been used to treat a variety of malignant tumors, including melanoma, lung cancer, renal cell cancer, head and neck cancer, Hodgkin’s disease, urothelial cancer (Ribas and Wolchok, 2018; Xiao et al., 2020) and CRC with deficient mismatch repair (dMMR) or microsatellite instability-high (MSI-H).