ATR and cancer: Third, cancer and precancer cells usually deal erroneously with damaged DNA, either not signaling the lesions correctly (e.g., due to the lack of p53, RB1, ataxia telangiectasia mutated (ATM), ataxia telangiectasia and Rad3 related (ATR), etc.), or due to alterations on the DNA repair mechanisms (caused by mutations such as BRCA1, BRCA2, and RAD51) [6, 7].