PDCD1 and melanoma: Although immune checkpoint inhibitors (ICIs) such as anti-PD-1/PD-L1 therapeutic antibodies like Nivolumab and Atezolizumab achieve remarkable benefits for many types of cancer, including melanoma and lung cancer, etc., identification of predictive biomarkers for anti-PD-1 therapy is one of the major challenges in developing effective ICI therapies for cancer treatment.