KRT14 and breast cancer: Next, we interrogated the embryonic-enriched mammary epithelial signature expression in mammary tumors that formed in mouse strains in which Brca1 had been deleted in either mammary epithelial luminal progenitors (Blg-Cre Brca1f/f p53+/-) or in basal cells, including basal stem cells (K14-Cre Brca1f/f p53+/-) [12], to determine whether the embryonic signature is activated in a validated mouse model of triple-negative breast cancer [31].