Biomarker discordance pre and post neoadjuvant chemotherapy in breast cancer

With the increasing use of neoadjuvant chemotherapy it is increasingly being observed that differences in the status of molecular markers may exist between core biopsy specimens and the residual disease in the breast post chemotherapy. Several hypotheses have been postulated to explain the biomarker discordance observed following neoadjuvant chemotherapy including intratumor heterogeneity, technical variance in the assays used to assess biomarkers and a genetic switch in the biology of the disease. Here we review published data looking at discordance of biomarkers following neoadjuvant chemotherapy and the prognostic and therapeutic implications of the observed discordance. We will review some of the biological explanations to account for the observed discordance and will look at its impact on the role of the pathologist as well as propose essential components required in a pathology report issued for patients receiving neoadjuvant chemotherapy that would help the medical oncologist in treatment planning.