BRCA1-mutant HCC1937 breast cancer cells were more sensitive to cisplatin, but less sensitive to doxorubicin and paclitaxel, than BRCA1-proficient MCF7 and MDA-MB-231 cells, as determined by the MTT test. Transfection of the wild-type BRCA1 in HCC1937 cells decreased their sensitivity to cisplatin, but restored sensitivity to doxorubicin and paclitaxel; this effect was at least in part attributed to the modulation of the apoptotic response. This evidence concerns the gene BRCA1 and breast cancer.