Breast cancers (BCs) are the most commonly diagnosed malignancies worldwide and are very heterogeneous solid tumors classified by immune-histochemical studies into three major types: estrogen receptor (ER) and progesterone receptor (PR) positive, human epidermal growth factor receptor 2 positive (HER-2+), and triple-negative breast cancers (TNBCs) [1]. The gene discussed is ESR1; the disease is breast cancer.