Changes in HER2 Amplification Status for Breast Cancer Patients After Immunohistochemistry Directed In Situ Hybridization.

The 2018 ASCO/CAP guidelines for HER2 testing for breast cancer implemented the addition of immunohistochemistry (IHC) directed in situ hybridization (ISH) recount to resolve equivocal results. The implementation of an additional 2+ IHC-directed ISH recount adds additional complexity to the testing workflow for an unclear impact on HER2 results. A retrospective review of all equivocal ISH cases (groups 2, 3, and 4) that underwent 2+ IHC-directed ISH, since the 2018 guidelines, which were finalized as either amplified or not amplified, was performed.

Quantitative Imaging Analysis Fluorescence In Situ Hybridization Validation for Clinical HER2 Testing in Breast Cancer.

Context.—: Quantitative imaging is a promising tool that is gaining wide use across several areas of pathology. Although there has been increasing adoption of morphologic and immunohistochemical analysis, the adoption of evaluation of fluorescence in situ hybridization (FISH) on formalin-fixed, paraffin-embedded tissue has been limited because of complexity and lack of practice guidelines.