TP53 and cancer: As an initiating event, DNA damaging agents used in cancer treatment generate DNA single- or double-strand breaks at telomeres [61] and in other chromosomal regions [62], activating a DDR via ATM, DNA-PKcs, ATR, CHK1, and CHK2 and/or other signaling kinases that converge at the tumor suppressor p53, resulting in cell cycle arrest [63].