ESR1 and breast neoplasm: Transcriptome analyses have reclassified breast tumors into intrinsic subtypes, such as normal breast-like, luminal A and luminal B (Estrogen Receptor (ER) + and/or Progesterone Receptor (PR) +), Human Epidermal Growth factor receptor 2 (HER-2) enriched, claudin-low, and basal-like, following the American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) classification [8,9].