BRCA1 and breast cancer: Moreover, while normal mammary epithelial cells (HME) expressing mutant RasV12 or overexpressing IRIS develop mammary tumors in SCID mice, unlike RasV12-driven tumors that showed luminal phenotype and expressed ERα and BRCA1 proteins [14, 17], IRISOE-driven tumors contained a large necrotic/hypoxic core [14], showed mesenchymal phenotype and were more aggressive.