Since it was previously reported that PD-1 blockade increases the number of tumor-infiltrating CD8+ T cells in mice bearing MC38 tumors15, and the number of tumor-infiltrating CD8+ T cells was associated with improved prognosis16–18, tumor-infiltrating CD8+ T cells are thought to have an important role in the effects of anti-PD-1 antibody treatment. Here, PDCD1 is linked to neoplasm.