Abstract P3-05-01: Accurate assessment of HER2 status in “triple-negative” breast cancer requires both IHC and FISH testing

Introduction: Triple-negative invasive breast carcinoma (TNBC) does not over-express estrogen, progesterone receptors and HER2/neu. Approximately 15% breast cancers are “triple negative” and have poor overall survival with no targeted therapeutic options. HER2 positive patients also have a poor prognosis which is markedly improved with anti-HER2 therapy. ASCO/CAP guidelines have made substantial improvement in biomarker assessment by standardizing pre-analytic, analytic and post-analytic variables. Since 2009, we have performed HER2 fluorescence in situ hybridization (FISH) analysis in addition to immunohistochemistry (IHC) on all triple negative patients in an effort to accurately assess HER2 status. Materials and Methods: Pathology database at our institute was queried for triple negative breast cancer cases 2009-2012. 175 cases were identified with ER(SP1; Ventana) = 2 was classified as HER2 positive. FISH for HER2 amplification was performed using the FDA-approved HER2 DNA Probe Kit (Vysis, Inc.). The hybridization results were recorded and analyzed by BioView Duet system (Allegro Plus Automated Scanner) with HER2 application software (BV-HER2-AF). Fisher9s exact test was performed to correlate HER2 amplification with clinico-pathological parameters. Results: 175 breast cancers were classified as “triple-negative” by IHC between 2009-2012. The patients’ age ranged from 25 to 93 years old (mean = 58); 109 were Caucasian (62%), 33 African American (19%), 9 Asian (5%) and 4 Hispanic (2%). The majority of the cases (152, 86%) were invasive ductal carcinoma. The rest include 9 cases of medullary carcinoma, 3 cases of metaplastic carcinoma, 3 cases of apocrine carcinoma, 2 cases of papillary carcinoma and 2 cases of invasive lobular carcinoma. 34 had regional lymph node (axillary) metastasis (19%) and 9 had distant metastasis (5%). 23 of the 175 “triple-negative” cases (13%) showed HER2 amplification by HER2 FISH analysis (HER2/CEP17> = 2). 14.9% (20/134) TNBC cases were FISH positive 2009-11 (HercepTest®, DAKO) and 7.3% (3/41) cases were FISH positive in 2012 (4B5, Ventana). 14 of the 23 patients were Caucasian (61%), 4 African American (17%), 2 Asian and 1 Hispanic. 20 of the 23 cases (87%) had invasive ductal carcinoma, of which 18 (78%) were poorly differentiated. 8 of the 23 cases (35%) had lymph node metastasis and 1 case had distant metastasis. No statistically significant correlation was observed between the HER2 gene amplification and clinicopathological factors analyzed, including race (P = 1), age (P = 1), tumor size (P = 0.6), pathologic stage (P = 0.6), lymph node status (P = 0.08), and Ki-67 index (P = 0.8 with 20% cutoff; P = 0.1 with 70% cutoff). Conclusion: In this cohort, 13% TNBC were re-classified as HER2 positive by performing HER2 FISH test in addition to immunohistochemistry analysis. Rate of FISH positivity in TNBC declined over the four year study period. No clinicopathological variables are correlated with HER2 FISH amplification. These data suggest that dual testing of HER2 should be considered routinely in TNBC for accurate classification to guide therapy. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P3-05-01.