ESR1 and breast cancer: Both K14-Cre;Brca1fl/fl;Wwoxfl/fl and K14-Cre;Brca1fl/fl;Wwoxfl/fl;Trp53+/fl mammary tumors exhibited a basal-like morphology with occasional expression of K14 [42] and lack of ER expression (Fig. 1C), suggesting a worse prognosis recapitulating human BLBC/TNBC.