FAS (Fas cell surface death receptor) is a member of the tumor necrosis factor receptor (TNFR) family, crucially involved in regulating programmed cell death (apoptosis). It is primarily expressed on the cell membranes of various cell types and, through binding with its ligand FASL, activates downstream signaling pathways leading to cell apoptosis. The FAS/FASL system plays an important role in maintaining immune self-tolerance, controlling inflammatory responses, and clearing tumor cells. The specific expression of the FAS gene and functional mutations are closely associated with the development of various diseases, including autoimmune diseases, tumors, and certain genetic disorders. Mutations or dysregulation in expression can lead to abnormalities in the apoptosis pathway, affecting tissue homeostasis and disease progression.