PRF1 and neoplasm: The mechanism by which CTLs kill tumor cells involves the following three aspects (1): the granular exocytosis pathway, via the synaptic exocytosis of cytotoxic granules that contain perforin and granzymes into the target, results in tumour cell destruction (2); the cytotoxic cytokine pathway, secretes cytokines, including IFN-γ and TNF-α (3); and CTLs are capable of eliminating target T cells via a chain reaction that results in apoptosis via the FAS ligand (FASLG) molecule (30, 31).