ER-positivity is also associated with better prognosis after breast cancer diagnosis than ER-negativity [14, 15], while human epidermal growth factor receptor 2 (HER2)-positivity [16] and triple negativity (ER-negative, progesterone receptor (PR)-negative, and HER2-negative) [17] are each associated with worse prognosis. Here, ESR1 is linked to breast cancer.