BRCA1 and breast cancer: In addition, the epigenetic silencing of BRCA1 was demonstrated to be excluded in hereditary ovarian cancers, and cancers with epigenetic BRCA1 silencing did not exhibit BRCA1 protein expression by immunohistochemistry.40 Furthermore, BRCA1 hypermethylation conferred the same degree of sensitivity to PARP inhibitors as did BRCA1/2 mutations in a breast cancer cell line.