PDCD1 and neoplasm: In addition to PD-1/PD-L1, various studies have showed that tumour-infiltrating lymphocytes (TILs) in and around neoplastic cells reflect host immunity in a range of cancers, such as breast cancer (77), gastric cancer (78), and NSCLC (79), and that the density of TILs (mainly T cells and NK cells) is associated with clinical prognosis (77–81).