FASLG (Fas ligand) is a cytokine that functions as a death-inducing ligand mediating apoptosis through the extrinsic apoptotic signaling pathway 1. When FASLG binds to its Fas receptor, it activates a caspase-mediated cascade that induces programmed cell death in target cells, characterized by DNA degradation and morphological changes 2. FASLG is typically expressed on T cells and natural killer cells, enabling them to eliminate target cells 3. Loss-of-function mutations in FASLG cause hyper-proliferation and autoimmune disorders, while exaggeration of its death-inducing capacity causes tissue destruction 2. Clinically, FASLG dysregulation associates with multiple diseases. Mutations in FASLG cause autoimmune lymphoproliferative syndrome 4, while polymorphisms (particularly rs5030772) correlate with alopecia areata susceptibility 5. The T844C polymorphism associates with increased breast cancer risk, especially in Asian populations 6. In tumor biology, FASLG copy number increases may facilitate immune evasion by reducing T-cell infiltration effectiveness 3. Beyond immune regulation, FASLG has expanded roles in angiogenesis and tumor progression 7, suggesting therapeutic potential as a drug target for enhancing anti-tumor immunity.