Abstract P2-04-10: Utility of simultaneous HER2 protein and gene assessment for the evaluation of discrepancy and intratumoral heterogeneity of HER2 status and the prediction of prognosis in invasive breast cancer using the gene-protein assay (GPA)

Abstract

Abstract Background: The eligibility of patients for HER2-targeted therapies is determined by the evaluation of HER2 gene amplification and HER2 protein overexpression. The gene-protein assay (GPA, Ventana Medical Systems, Inc., USA) is a new method for simultaneous evaluation of HER2 immunohistochemistry (IHC) and dual in situ hybridization (DISH) using a single tissue section. In this study, we investigated the relationship between HER2 IHC and DISH results evaluated by GPA. In addition, we analyzed the correlation between HER2 status and prognosis of invasive breast cancer patients. Patients and Methods: In this study, invasive carcinoma tissues of 280 consecutive patients treated in Saitama Cancer Center in 2000-2001 (median follow-up: 130 months) were examined. Among HER2 positive initial samplings, no patients originally received adjuvant trastuzumab therapy. However, 76% of HER2 positive cases of recurrence received trastuzumab therapy. GPA was performed on a section of routinely processed primary tumor and the status of HER gene and protein were separately evaluated in whole areas of tumor sections using the following FDA criteria: DISH (negative: HER2/CEN17 < 2, positive: HER2/CEN17 ≥ 2.0) and IHC (score 0 to 3+). In IHC score 2+ patients group, final HER2 positivity was decided according to DISH results using criteria of FDA criteria. Recurrence-free survival (RFS) and cancer-specific survival (CSS) stratified by IHC and DISH results were analyzed. In addition, patterns of heterogeneity were grouped according to the following 4 phenotypic and genotypic types: A) IHC 2+/DISH+; B) IHC 2+/DISH-; C) IHC 1+ & 0/DISH+; and D) IHC 1+ & 0/DISH-. The presence of heterogeneity in relation to prognosis was analyzed in the IHC 0 & 1+/DISH- group. Results: The HER2 IHC 3+ group (27.5%), both with or without trastuzumab therapy, had significantly worse survival than HER2 IHC 1+ & 0 group (RFS: P=0.0039; CSS: P=0.0362) and HER2 DISH+ group (27.5%) had significantly worse survival than HER2 DISH- group (RFS: P=0.0056; CSS: P=0.0497). HER2 positive group defined by FDA criteria had significantly worse RFS than HER2 negative group (P=0.0211). HER2 IHC 1+ & 0/DISH+ group had significantly worse RFS than IHC 1+ & 0/DISH- group (P=0.0208). In the HER2 IHC 1+ & 0/ DISH- group, patients with heterogeneity (33 cases) had significantly worse survival than those without heterogeneity (RFS: P=0.0176; CSS: P=0.0199). Conclusions: HER2 GPA technology might be useful for evaluating the discrepancy and heterogeneity of HER2 IHC and DISH results at single cell levels simultaneously and the presence of HER2 tumor cell heterogeneity might be a potent prognostic factor in HER2 negative breast cancer patients. Further clinical research must be conducted for clarification of the relationship between the presence of HER2 intratumoral heterogeneity and the effectiveness of HER2-targeted therapies. Citation Format: Sasagu Kurozumi, Mary Padilla, Masafumi Kurosumi, Hiroshi Matsumoto, Yuji Hayashi, Katsunori Tozuka, Shigenori E Nagai, Kenichi Inoue, Hanako Oba, Jun Horiguchi, Izumi Takeyoshi, Jim Ranger-Moore, Eslie Dennis, Hiroaki Nitta. Utility of simultaneous HER2 protein and gene assessment for the evaluation of discrepancy and intratumoral heterogeneity of HER2 status and the prediction of prognosis in invasive breast cancer using the gene-protein assay (GPA) [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 P2-04-10.