Based on pathological features with human estrogen receptor (ER), progesterone receptor (PR), and epidermal growth factor 2 (HER2), breast cancer is categorized into three subtypes: luminal breast cancer (ER/PR+, HER2–), HER2‐positive breast cancer (HER2+), and triple‐negative breast cancer (TNBC) (ER–, HER2–, PR–).3 This evidence concerns the gene ESR1 and breast cancer.