BRCA1 and ovarian cancer: Using an siRNA screen, we found that (1) of all the E2F family members, only E2F4 depletion reduced BRCA1 expression in OVCAR-8 cells; (2) BRCA1 expression in multiple ovarian cancer cell lines was reduced by two independent E2F4 siRNAs; (3) E2F4 depletion in short-term ex vivo cultures of freshly isolated HGSOC tumors from mouse PDX models reduced BRCA1 expression; and (4) E2F4 expression is positively correlated with BRCA1 expression in primary HGSOCs and ovarian cancer PDXs.