ESR1 and breast cancer: BC is characterized based on the prediction analysis of microarrays 50 (PAM50) using the variation of the gene expression of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) into Luminal A, Luminal B, HER2-enriched, basal-like (triple negative), and Normal like [20, 33, 37].