Institutional quality assurance for breast cancer HER2 immunohistochemical testing: identification of outlier results and impact of simultaneous fluorescence in situ hybridization cotesting

The College of American Pathologists Accreditation Checklist requires comparison of laboratory predictive results with published benchmarks but does not require analysis of individual pathologists. With the availability of targeted human epidermal growth factor receptor 2 (HER2) protein therapy, uniform reporting of HER2 protein status by immunohistochemistry (IHC) is essential. Our aim was to compare HER2 IHC results among pathologists in routine clinical practice within a single institution and assess the impact of simultaneous IHC and fluorescence in situ hybridization (FISH) ordering. We reviewed reports from 928 consecutive breast needle biopsies from 2008 to 2012 at a tertiary academic medical center in which HER2 IHC and HER2 FISH were ordered. There was a significant association between breast pathologist and IHC result (negative, 49.8%-83.2%; positive, 8.7%-14.1%; equivocal, 5.2%-41.5%; P < .0001) but not breast pathologist and FISH result (P = .69). For 1 pathologist, IHC signed out with FISH had an equivocal rate nearly 2-fold lower than IHC results that were reported first (10.5% versus 20.9%) (P = .04). Institutions should be aware that although overall HER2 IHC reporting may be consistent with guidelines, there can be significant variation among practitioners. In addition to aggregate data, we recommend comparing the rates from individual pathologists to standards. Furthermore, routine simultaneous ordering of both IHC and FISH could impact interpretation of test results and may inappropriately encourage less confidence in IHC results among pathologists.