Fitzgibbons, Patrick L.

Abstract Context. —Intratumoral heterogeneity of HER2 gene amplification has been well documented and represents subclonal diversity within the tumor. The reported incidence of intratumor HER2 amplification genetic heterogeneity ranges in the literature from approximately 5% to 30%. The presence of HER2 genetic heterogeneity may increase subjectivity in HER2 interpretation by the pathologist. Objectives. —To define HER2 genetic heterogeneity and to provide practice guidelines for examining and reporting breast tumors with genetic heterogeneity for improvement of HER2 testing in breast cancer. Design. —We convened an expert panel to discuss HER2 gene amplification testing by fluorescence in situ hybridization. Components addressed included a definition of HER2 amplification heterogeneity, practice guidelines for examination of the tissue, and reporting criteria for this analysis. Results. —Genetic heterogeneity for amplification of HER2 gene status in invasive breast cancer is defined and guidelines established for assessing and reporting HER2 results in these cases. These guidelines are additive to and expand those published in 2007 by the American Society of Clinical Oncology and the College of American Pathologists. Conclusion. —Standardized methods for analysis will improve the accuracy and consistency of interpretation of HER2 gene amplification status in breast cancer.

Context.— The American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) published guidelines in 2007 regarding testing accuracy, interpretation, and reporting of results for HER2 studies. A 2008 survey identified areas needing improved compliance. Objective.— To reassess laboratory response to those guidelines following a full accreditation cycle for an updated snapshot of laboratory practices regarding ASCO/CAP guidelines. Design.— In 2011, a survey was distributed with the HER2 immunohistochemistry (IHC) proficiency testing program identical to the 2008 survey. Results.— Of the 1150 surveys sent, 977 (85.0%) were returned, comparable to the original survey response in 2008 (757 of 907; 83.5%). New participants submitted 124 of 977 (12.7%) surveys. The median laboratory accession rate was 14 788 cases with 211 HER2 tests performed annually. Testing was validated with fluorescence in situ hybridization in 49.1% (443 of 902) of the laboratories; 26.3% (224 of 853) of the laboratories used another IHC assay. The median number of cases to validate fluorescence in situ hybridization (n = 40) and IHC (n = 27) was similar to those in 2008. Ninety-five percent concordance with fluorescence in situ hybridization was achieved by 76.5% (254 of 332) of laboratories for IHC − findings and 70.4% (233 of 331) for IHC + cases. Ninety-five percent concordance with another IHC assay was achieved by 71.1% (118 of 168) of the laboratories for negative findings and 69.6% (112 of 161) of the laboratories for positive cases. The proportion of laboratories interpreting HER2 IHC using ASCO/CAP guidelines (86.6% [798 of 921] in 2011; 83.8% [605 of 722] in 2008) remains similar. Conclusions.— Although fixation time improvements have been made, assay validation deficiencies still exist. The results of this survey were shared within the CAP, including the Laboratory Accreditation Program and the ASCO/CAP panel revising the HER2 guidelines published in October 2013. The Laboratory Accreditation Program checklist was changed to strengthen HER2 validation practices.