To test the hypothesis that triple-negative breast cancers are sensitive to Chk1 inhibitors in the absence of cytotoxic chemotherapy agents, a panel of sporadic triple-negative and luminal breast cancer cell lines [31] as well as several ovarian cancer cell lines were tested for their sensitivity to V158411 and compared against a panel of cell lines derived from cancers of the lung, colon or prostate. This evidence concerns the gene CHEK1 and breast cancer.