One of the most important ways CTL plays its role in killing tumor cells is by secreting a variety of important cytokines, mainly via three pathways: cell lysis caused by perforin/granulose, tumor cell apoptosis caused by cytokines FasL/TNF-α/LT-α/FasL, and immunoregulatory effects induced by IFN-γ and IL-2. This evidence concerns the gene PRF1 and neoplasm.