ESR1 and breast cancer: Several studies have shown that women with the breast cancer 1 (BRCA1) gene mutation present breast cancer with a genetic expression pattern that is compatible with the basal subtype.5,30-33 However, the multistage process of carcinogenesis in the breast epithelium of women with genetic abnormalities who are highly susceptible to carcinogenesis would not depend on ER or HER2 protein expression, since the stimuli required for cell proliferation would be determined by the abnormalities present in the cell genome.