ESR1 and basal-like breast carcinoma: Basal-like tumors are defined by high expression of cytokeratins 5/6 and 17, low expression of the estrogen receptor (ER) and HER2 receptor, and aberrant global DNA hypermethylation [9,10] Clinically, basal-like breast cancer (BLBC) is associated with a more aggressive and metastatic behavior with a poorer prognosis and shorter survival time, and has a higher prevalence among premenopausal African American women [10,11].