After activation, cytotoxic lymphocytes induce apoptosis of tumor cells by releasing perforin (a protein homologous to complement protein C9, present in cytoplasmic granules of NK and CD8 T cells, induces the formation of transmembrane pores in target cells, allowing entry of granzymes), granzymes (serine protease released by exocytosis and in contact with the target cell cleaves and activates caspases that induce apoptosis of these cells) and FAS/FAS-L (FAS ligand—induces cell death when FAS binds to FAS-L expressed on activated CD8 cells) [18–20]. The gene discussed is PRF1; the disease is neoplasm.