Breast cancer can be divided into three types: hormone receptor-positive (estrogen receptor (ER) or progesterone receptor (PR)) constitutes 70% of breast cancer cases, ERBB2-positive constitutes 15–20% of breast cancer cases and triple negative breast cancer (ER−, PR− and ERBB2−) constitutes 15% of breast cancer cases [2]. The gene discussed is ESR1; the disease is breast cancer.