Based on the expression of 3 biomarkers (estrogen receptor ER, progesterone receptor PR and human epidermal growth factor receptor Her2), we can classify breast cancer into 4 major intrinsic molecular subtypes; luminal A (ER + or PR + , Her2 −), luminal B (ER + or PR + , Her2 +), Her2 + (ER −, PR −, Her2 +) and triple negative (ER −, PR −, Her2 −) breast cancer [2, 3]. The gene discussed is ESR1; the disease is breast cancer.