PRF1 and neoplasm: TILs are primarily composed of T lymphocytes (24), including CD8+ cytotoxic T cells that mediate tumor cell lysis through perforin–granzyme pathways (25, 26), CD4+ helper T cells (Th1/Th2) that regulate cellular and humoral immunity via IL-2/IFN-γ and IL-4/IL-5, respectively, and Foxp3+ Tregs that exert immunosuppressive effects through IL-10 and TGF-β secretion (27–29).