PRF1 and neoplasm: In lymphocytes, B cells can act as antigen-presenting cells and secrete cytokines to exert anti-tumor effects (24); Cytotoxic T lymphocytes (CTLs) can specifically recognize tumor-associated antigens through major histocompatibility complex (MHC) I on their surface, bind to tumor cells and produce perforin and other cytotoxins to kill cancer cells (25); Natural killer (NK) cells have no MHC or human leukocyte antigen restriction and can release perforin, granzyme and cytokines to destroy tumor cells (26).