ATR and cancer: Moreover, our analysis confirmed the AEP/ATR ratio as an efficient predictive biomarker for the stratification of responder (AEPlow/ATRhigh, AEPlow/ATRlow or AEPhigh/ATRhigh) and nonresponder (AEPhigh/ATRlow) patients (Fig. 6D), further supporting an unexpected connection between AEP and ATR levels in genotoxic tolerance in cancer cells (Fig. 5).