In contrast, ER+ breast cancers could be classified into luminal A and luminal B subtypes with significantly distinct prognosis, luminal A tumors displayed favorable outcome, whereas survival of patients with luminal B tumors was poor and comparable to those of the ER negative ErbB-2 and basal subtypes.2 The molecular classifications are found to be strongly associated with ER status and moderately associated with grade, but not associated with menopausal status, nodal status, or tumor size.3 This evidence concerns the gene ESR1 and breast cancer.