CDKN1A and neoplasm: In response to therapeutic doses of ionizing radiation (2 Gy and above), however, the WIP1 effect precedes full repair, p21 blocks apoptosis, and p53 becomes up- and down-regulated sequentially until either the damage is reduced to a level compatible with cell survival or adaptation [152], or the cells undergo one of the available “death” options which is commonly p21-mediated SIPS but may also include apoptosis, necroptosis [153] and autophagy [154,155] which may contribute significantly to the response of some types of tumor cells to ionizing radiation.