Abstract P4-15-22: The ASCO/CAP guideline update for HER2 testing increases the number of breast cancer patients eligible for HER2-targeted therapy

Abstract

Background: The American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) published, in Nov/2013, the interpretive guidelines for HER2 testing of breast cancer patients. This aimed to improve the accuracy of HER2 testing and its utility as a predictive marker in invasive breast cancer. The former version of these criteria was written in 2007. Objectives: to compare the HER2 immunohistochemical (IHC) analysis using the 2007 versus 2013 algorithms in a cohort of breast cancer cases diagnosed in a single institution in Southern Brazil. The cases were previously classified as HER2 1+ or 2+, using the 2007 criteria. Methods: the sample included 100 invasive breast cancer cases. The HercepTest (Dako, Denmark) was used for determination of HER2 expression. The HER2 testing was analyzed independently by two pathologists. The FISH analysis was done using a HER2/D17Z1 probe set. Preliminary Results: The HER2 IHC interpretation changed in 11/69 (15.9%) cases: 8.7% negative or equivocal cases by the 2007 guidelines were positive by the 2013 classification and 7.2% of HER2 1+ cases became equivocal (p<0.001; x2 test). The FISH analyses are ongoing. Conclusion: The 2013 ASCO/CAP guidelines resulted in less negative cases and in more equivocal (requiring reflex testing) and positive tests. Applying the ASCO/CAP 2013 guidelines resulted in a significantly increase of breast cancer patients eligible for HER2-targeted therapies. Citation Format: Juliana Giacomazzi, Carolina R Hartmann, Diego D Paskulin, Luis Fernando Rivero, Maira Caleffi, Alessandro C Pasqualotto, Marcia S Graudenz, Daniela D Rosa. The ASCO/CAP guideline update for HER2 testing increases the number of breast cancer patients eligible for HER2-targeted therapy [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P4-15-22.