A Comparative Analysis of the Value of HER2 Immunohistochemistry Scoring in Primary and Metastatic Breast Cancer, in the Era of HER2 "Low" Breast Cancers.

Abstract

BackgroundIn the DESTINY-B04 trial, patients with pretreated HER2 low metastatic breast cancer (defined as immunohistochemistry score of 1+ or 2+ and negative in situ hybridization) had significant survival improvement with Trastuzumab therapy. MethodsThe goal of our study was to compare the HER2 immunohistochemistry scores of paired primary and metastatic breast cancer, with emphasis on HER2 low criteria and its implications for detailed immunohistochemistry interpretation. Using the pathology database from 2011, we identified 272 cases of primary breast cancers with paired metastases. We reviewed and performed immunohistochemistry concordance between the primary and metastases and calculated the HER2 low incidence. ResultsCompared to the primary, HER2 immunohistochemistry score in the metastases remained the same in 156/272 cases (57%) and by immunohistochemistry was: 0 (67/114=59%), 1+ (22/52=42%), 2+ (34/67=51%), 3+ (33/39=85%) and HER2 low (85/119=71%). The HER2 score changed from 0 to HER2 low in 46 cases (17%) and vice versa in 30 (11%). ConclusionsThe concordance rate of HER2 immunohistochemistry scores was 57%, highest in 3+ cases, followed by HER2 low and then HER2 negative. The incidence of HER2 low was higher in the metastases by 6% compared to the primary. HER2 should be tested in all metastases and compared with the primary, due to differences in scores as seen in 28% of our cases, which may have clinical implications in the new HER2 low era.