BRCA1 and breast cancer: The screen was performed on the breast cancer cell line MDA-MB-231, which carries several typical features of BRCA1-deficient breast cancers, for example, expression of basal epithelial markers, negativity for hormone receptors, and a high metastatic potential.20 Cells transfected with siRNA against BRCA1 (siBRCA1) or non-targeting control siRNA (siCtrl) were grown in the presence of chemical compounds at five different concentrations in 384-well plates for 3 days.