ATR and cancer: Compared to ATM, ATR usually copes with wider DNA damage problems and replication stress to maintain genomic integrity and cell survival.[17, 18] As anti‐tumor factors, genes in the ATM pathway frequently lose copies or are mutated in cancer cells, whereas genes in the ATR pathway are rarely mutated.[19, 20, 21, 22, 23, 24] Consequently, the ATR pathway may be particularly important for tumor cell survival, such as TNBC, which is characterized by the deficiency of the DDR pathway because of mutations of DDR genes, including BRAC1/2, p53, and ATM.