PRF1 and cancer: NK-exos typically contain cytotoxic proteins (e.g., granzyme B, perforin, FasL, and TRAIL), originating from NK cells, which exert potent tumor-killing effects against various cancers (e.g., melanoma, breast cancer, neuroblastoma, lung cancer, pancreatic cancer, and liver cancer) [15,16,17,18,19,20].