Irradiation exerts an immunostimulating activity by increasing NK cell cytotoxicity and tumor infiltration by CD8+ cytotoxic T lymphocytes, the accumulation of tumor-associated M1 macrophages (inhibiting tumor growth), reducing the level of infiltrating regulatory T cell (Treg) lymphocytes [65], enhancing the expression of Fas and IFN-γ, and the inhibition of the PD-1/PDL-1 pathway [66]. Here, FAS is linked to neoplasm.