On the other hand, BRCA1-defective breast cancer cells were significantly less sensitive to doxorubicin (Dox) (IC50 : 45–50 μM) compared with MCF-7 (IC50 : 1–5 μM) and MDA-MB231 (IC50 : 5–10 μM) (P<0.02), as well as to paclitaxel (Tax) (IC50 : >2 μM for HCC1937, 0.1–0.2 μM for MCF-7 and 0.01–0.02 μM for MDA-MB231) (P<0.001). This evidence concerns the gene BRCA1 and breast cancer.