Comparative study of spatial localization of HER-2 and CEP17 signals and of HER-2/CEP17 ratios, in “thin” and “thick” tissue sections

One presumed drawback of performing fluorescence in situ hybridization on routine tissue sections for HER-2 status evaluation in breast carcinomas is nuclear truncation. Therefore, HER-2/CEP 17 ratios were compared in routine (4 μm) vs. thicker (15 μm) tissue sections. Additionally, the distances of both signals from the nuclear center were measured by three-dimensional image analysis. HER-2 and CEP 17 signals’ number increased in thick sections; however, HER-2/CEP 17 ratios were decreased. This could be attributed to a preferential increase in CEP17 signals explained by their more peripheral localization and apparent "loss" in truncated nuclei. The aforementioned decrease of HER-2 ratios did not alter HER-2 status except in cases in the equivocal category where it changed from equivocal to non-amplified. Thus, at least a subset of the equivocal cases could represent an artifactual increase of HER-2 ratio related to nuclear truncation and loss of peripheral CEP 17 signals in routine sections.