Interestingly, studies using PCa cell lines have shown that ATM loss does not increase sensitivity to PARPi but rather to ataxia telangiectasia and RAD3-related (ATR) inhibition57 and the first clinical trial of the ATR inhibitor BAY 1895344 confirmed antitumor activity in ATM-deficient cancer patients.58 In addition, ATR inhibitors showed antitumor activity in cancers with BRCA1 mutations that were resistant to PARPi.58 Therefore, it is important to carefully analyze the mutation status of the individual HRR genes to make a personalized treatment decision. The gene discussed is ATR; the disease is cancer.