Z-VAD is a competitive, irreversible pan- caspase inhibitor. Z-VAD inhibits all 10 caspases, except for caspase-2 which is only weakly inhibited. Z-VAD decreases radiation-induced apoptosis. Z-VAD induces both autophagy and necrosis in irradiated MDA-MB-231 and H460 mouse xenografts. Z-VAD with radiation produces a significant tumor growth delay and shows dramatic antiangiogenic effect in cancer xenograft.