Fas, also known as APO-1, or CD95, is a cell-surface receptor that transduces apoptotic signals from Fas ligand (FasL) .Fas forms the death-inducing signaling complex (DISC) upon ligand binding. Membrane-anchored Fas ligand trimer on the surface of an adjacent cell causes oligomerization of Fas. Recent studies which suggested the trimerization of Fas could not be validated. Other models suggested the oligomerization up to 5-7 Fas molecules in the DISC.Although Fas has been shown to promote tumor growth in the above mouse models, analysis of the human cancer genomics database revealed that FAS is not significantly focally amplified across a dataset of 3131 tumors (FAS is not an oncogene), but is significantly focally deleted across the entire dataset of these 3131 tumors, suggesting that FAS functions as a tumor suppressor in humans.In cultured cells, FasL induces various types of cancer cell apoptosis through the Fas receptor. In AOM-DSS-induced colon carcinoma and MCA-induced sarcoma mouse models, it has been shown that Fas acts as a tumor suppressor.Furthermore, the Fas receptor also mediates tumor-specific cytotoxic T lymphocyte (CTL) anti-tumor cytotoxicity. Serum Fas has been reported to be elevated in cancer patients, possibly originating in the tumor cell itself , and in autoimmune diseases.