FAS and neoplasm: In addition, radiation therapy exerts an immunostimulating activity by increasing NK cell cytotoxicity, facilitating the infiltration and accumulation of CD8+ T cells and tumor-associated M1 macrophages (inhibiting tumor growth), reducing the infiltration of Tregs (71), enhancing the expression of Fas and IFN-γ, and inhibiting the PD-1/PD-L1 pathway (24, 27).