However, these percentages are higher in a subset of women with early-onset BC, familial history, or triple-negative BC (TNBC), i.e., estrogen and progesterone receptors (ER and PR, respectively) and human epidermal growth factor receptor 2 (HER2) negative, based on immunohistochemistry (IHC) [6, 7]. The gene discussed is ESR1; the disease is breast cancer.