Intertumoral heterogeneity of bifocal breast cancer: a morphological and molecular study

To analyze concordance rates between individual foci of bifocal BC for histological grade, type and intrinsic subtype based on immunohistochemical (IHC) and mRNA-testing using MammaTyper. We evaluated histological grade and type as well as intrinsic subtype based on IHC status for estrogen and progesterone receptors, HER2 and the mitotic activity index in 158 individual foci of 79 bifocal BC. A subgroup of 31 cases additionally underwent mRNA-based subtyping using the MammaTyper (MT) test. We calculated concordance rates between individual foci, as well as Cohen’s Kappa (k). For 79 bifocal BC, concordance rates between individual foci for grade, histological type, and IHC-based subtype were 69.6