The mechanism of this insensitivity has been investigated, and three conditions are thought to be necessary for anti-PD-1 antibody therapy to be effective: the infiltration of T cells into tumor tissue, the presence of immune cells expressing PD-1 and PD-L1 in tumor tissues, and the presence of a T cell population specifically recognizing tumor antigens.5 This evidence concerns the gene PDCD1 and neoplasm.