Current endocrine-based treatments targeting estrogen (E2)-ERα signaling (selective estrogen receptor modulators, selective estrogen receptor downregulation, aromatase inhibitors) [6, 7] as well as some molecular target drugs, such as mTOR inhibitors [8, 9], PI3K inhibitors [10], and CDK4/6 inhibitors [11–14], have been clinically applied for treating luminal-type breast cancer. The gene discussed is ESR1; the disease is breast cancer.