Using conventional immunohistochemistry (IHC) detection of estrogen receptor-alpha (ERα), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) status, molecular subtypes of breast cancer can be classified as: luminal A (ERα+ and/or PR+, HER2-), luminal B (ERα+ and/or PR+, HER2+), triple-negative (ERα-, PR- and HER2-), and HER2 (HER2+, ERα-, and PR-) [4]. The gene discussed is ESR1; the disease is breast cancer.