The IHC-based classification systems remain of use in clinical practice, particularly when fresh tissue is not available, and has been shown to correlate well with the intrinsic classification using gene expression by microarrays: ER/PR+ and HER2− with luminal A; ER/PR+ and HER2+ with luminal B; ER−, PR− and HER2+ with the HER2-overexpressing group; and ER−, PR− and HER2− with triple negative breast cancer (34–39). This evidence concerns the gene ESR1 and triple-negative breast carcinoma.