ATR and cancer: It is well-established that several pathway are cancer cells activated to promote DNA repair and cell survival in response to IR (20), such as cell cycle checkpoint activation, DNA repair pathway, ATM/ATR, PI3K/AKT, and MEK/ERK activation, which promotes survival of cancer cells through up-regulation of anti-apoptotic factors and down-regulation of pro-apoptotic factors (12, 21–24).