Breast cancer subtypes and molecular biomarkers

In the last decade, comprehensive whole genome expression profiling by microarray technology has extensively defined breast cancer into distinct molecular subtypes that differ in terms of patient outcome and response to systemic treatment. However, gene microarrays are expensive and several issues relating to data analysis, reproducibility and validation still need to be resolved before this technology is routinely adopted into the clinical setting. In this review, we discuss the role of established molecular markers currently used in the management of breast cancer. We outline recent evidence describing their use on immunohistochemical panels which may act as surrogates for gene expression profiling when subtyping breast cancers. We provide an overview of the emerging field of microRNAs and circulating tumour markers and their potential role as novel biomarkers. We propose that further research in the development of molecular markers will identify subtypes at the time of primary diagnosis and guide the challenges of individualized patient treatment and targeted drug design.