Together, these data showed that expression of a set of signatures composed of genes associated with the epithelial and the mesenchymal phenotypes (derived from HMLE, HMLER and lung cancer) reliably predicted poor outcome independent of the breast cancer subtype being ER+ or ER-, while NOS-TFs, mammaprint and the PCNA metagene signatures were not predictive or were restricted to ER+ tumors. This evidence concerns the gene ESR1 and breast cancer.