Both Colo829 and DU145 cells treated with either 3 × 8 Gy or a single dose of 16 Gy were resistant to NK cell cytotoxicity in vivo 72 h after RT because perforins released by NK cells failed to form functional pores in the membranes of irradiated cancer cells.197 Thus, combination therapies are necessary. This evidence concerns the gene PRF1 and cancer.