We previously discovered that the majority of p18−/− mice developed CK8+ and ER+ luminal type mammary tumors while most p18−/−;Brca1+/− mice formed mammary tumors that were ER− and CK5+ basal-like tumors expressing mesenchymal markers as well as EMT-TFs [11, 28, 31]. The gene discussed is ESR1; the disease is breast cancer.