BRCA1 and breast cancer: Here, we compare the breast cancer cell line HCC1937, carrying a protein-truncation mutation in one allele of BRCA1 while the other allele is lost, complemented with an empty plasmid (BRCA1null), with its isogenic counterpart expressing a wild-type BRCA1 cDNA (BRCA1wt) [43] (Fig. 2A).