Breast cancer is a heterogeneous disease.1 With the development of DNA microarray technology, breast cancers were divided into four subtypes: estrogen receptor (ER)+/luminal-like, basal-like, Erb-B2+ and normal breast-like.2 According to intrinsic properties and different outcomes of the tumors, ER+/luminal-like group was further classified into at least two subgroups: luminal A and luminal B+C subtypes.3 Different therapeutic strategies are applied according to the molecular features of each subtype. The gene discussed is ESR1; the disease is breast cancer.