Most BC samples overexpress hormone receptors (HR), including estrogen receptor (ER) and/or progesterone receptor (PR) [4, 5], whereas human epidermal growth factor receptor 2 (HER2) overexpression only occurs in 20–30% of cases [6]; thus, the most common BC subtype is HR+/HER2− [7]. The gene discussed is ESR1; the disease is breast cancer.