Impact of updated 2013 human epidermal growth factor receptor-2 testing guidelines on HER2 positive invasive breast cancer diagnosis: A three year retrospective study.

Abstract

e12554 Background: Breast cancer is a frequently diagnosed malignancy in the United States accounting for approximately 266,000 cases and 40,000 deaths annually. Human epidermal growth factor receptor 2 (HER2) is a surface protein shown to affect cell proliferation, migration and survival - the hallmarks of neoplastic cells. HER2 is overexpressed in 20-35% of breast cancer cases and has a strong prognostic and therapeutic significance. This discovery led to development of therapeutic agents targeting HER 2 receptor. In 2013, College of American Pathologists (CAP) updated their recommendations for HER2 testing by incorporating an algorithm with immunohistochemistry (IHC) and In situ hybridization (ISH). The primary objective of our study was to assess for variance in HER2 interpretation by applying the updated 2013 criteria to all diagnosed cases in our hospital for the immediate previous three years. Methods: We retrospectively reviewed charts of patients diagnosed with invasive breast carcinoma from January 1, 2010 to December 31, 2012 at our hospital. The new American college of pathology criteria assessing FISH HER2 copy number and HER2/CEP ratio for each patient was compared to the old criteria to assess for variance in HER2 interpretation. Categorical variables are presented as percentages and kappa statistic was used to assess for variance. Results: We reviewed 526 charts with an invasive breast cancer diagnosis over a 3-year period. 10.83% of patients were HER2 amplified, 86.12% were non-amplified and 3.04% were equivocal. Applying the updated 2013 CAP criteria, we found that 11.21% were amplified, 74.33% were non amplified, and 14.44% remained equivocal. Kappa statistic indicated substantial agreement (0.804) between the old and new criteria. A review of our cohort revealed an overall lower level of HER2 positive cases at 10.83% (old criteria) and 11.21% (updated criteria) when compared to historical studies. The increase in equivocal cases from 3.04% to 14.44% with the new criteria suggests under diagnosis of HER2 positive cases. Due to the lack of IHC performed (as per old standards), further classification of equivocal cases (based on new criteria) was not possible. While we saw some movement in our data from non-amplified to equivocal, our analysis indicated substantial statistical agreement between the old and the new diagnostic criteria Conclusions: Our study did not show a variance in HER2 interpretation between the 2007 and 2013 CAP criteria which is reassuring. An increase of 11.4% cases in the equivocal category was noted and may reveal a significant difference if further delineation is feasible. This variance could be important given the prognostic and therapeutic implications in HER2 positive breast cancer.[Table: see text]