AG014699 (PARP inhibitor) was highly cytotoxic against breast cancer cells with mutationally inactivated (MDA-MB-436) or epigenetically silenced (UACC3199) BRCA1, as determined by a clonogenic assay. BRCA1-deficient HCC1937 cells were more sensitive to AG014699 than the isogenic cell line with restored BRCA1 function (rhodamine B proliferation test). AG014699 and carboplatin efficiently inhibited growth of MDA-MB-436 and UACC3199 derived xenografted tumors. This evidence concerns the gene BRCA1 and breast cancer.