Molecular Taxonomy and Signatures of Breast Cancer in 2017

Breast cancers are best classified according to their level of hormone receptors and HER2 gene expression. Molecular classification has modified this simplistic taxonomy highlighting multiple profiles with different prognosis. It is in this context, and given the need to use targeted therapies, that molecular signatures were developed. Although they differ in methods (qRT-PCR, micro-array, or derivatives), molecular signatures endorse the same objectives: calculate a prognostic score based on the levels of gene expression involved in carcinogenesis, and, if possible, predict response to treatment. Applicable mainly to luminal ER-positive tumors, molecular signatures have proven their prognostic value in large prospective clinical trials and experts now look forward to integrate them in the therapeutic decision, which is currently based on clinico-pathological criteria. Furthermore, compared to the cost of chemotherapy, molecular signatures provide a real financial benefit and help to equilibrate the risk-benefit balance by reducing the use of aggressive treatments that are sometimes ineffective.