Significance of biomarker discordance in breast cancer from the pathologist's perspective.

Information on hormone receptor and human epidermal growth factor receptor 2 (HER2) is important for making optimal therapeutic decisions for breast cancer patients. Discordance in these biomarkers between primary breast carcinomas and corresponding metastases is well documented and may lead to changes in management option. The underlying mechanisms of biomarker discordance are complicated and multifactorial. Whereas biologic evolution, intratumoral heterogeneity, and subclonal selection may account for discordance, variations in sampling, processing, staining procedure and interpretation are the important contributory yet controllable factors. This article reviews the effects of different factors on the biomarker discordance, the clinical significance and the importance of standardizing methodology and interpretation criteria.