Abstract P2-08-18: Gene and protein expression profiles of HER2, ER, PR, and Ki67 in matched pair samples of primary (PBC) and metastatic breast cancer (MBC) tissues

Abstract

Abstract Background: The genotype and phenotype of breast cancer may change during disease progression. But technical issues may affect biomarker assessment when comparing primary tumor tissues with biopsies of metastasis at distant sites. As the exact determination of molecular subtype in primary tumors for prevention of distant metastasis is of the utmost importance in clinical decision making, we compared RNA expression levels of ESR1, PGR, ERBB2 and MKI67 in pairs of PBC and MBC tissue using RT-qPCR and evaluated our results against conventional immunohistochemistry (IHC). Methods: The tumor bank of a single institution was screened for paraffin-embedded pairs of PBC and MBC tissue samples and a total of 34 matched PBC and MBC pairs. RNA was extracted using a bead-based extraction method (RNXtract® IVD kits, BioNTech Diagnostics GmbH). Multiplex RT-qPCR was performed using TaqMan® based primer probe sets for ESR1, PGR, ERBB2 and MKI67 (MammaTyper® IVD kits, BioNTech Diagnostics GmbH). Results were compared with IHC analysis of ER (clone 1D5), PR (clone PgR636) and HER2 (A0485) in both primary and metastatic tissue. Associated survival data will be presented at the meeting. Results: Samples from 34 patients with MBC and PBC were available. Positivity of PBC for ER, PR & HER2 IHC was 71%, 76% and 7%, while positivity for RT-qPCR for ESR1, PGR and ERBB2 was 78%, 70% and 3%. The overall agreement between matched primary and metastatic lesions by IHC was 80%, 60% and 100% by IHC and 90%, 70% and 100% for RT-qPCR of ESR1, PGR and ERBB2. When comparing PBC with MBC the NPA was substantially lower for IHC (ER 56%, PR 50% and HER2 100%) than for RT-qPCR (ESR1 100%, PGR 100% and ERBB2 100%). Strikingly, there were some shifts from negative to positive for IHC based ER/PR determination, and from positive to negative for RT-qPCR, when comparing differences between PBC and matched MBC. By IHC several primary "non-luminal tumors" turned into metastatic "luminal" tumors exhibiting hormone receptor expression, while no such case was observed for RT-qPCR determination. Conclusion: Overall concordance between PBC and MBC is high, particularly when tested by RT-qPCR. As shifts from non-luminal to luminal and aggressive to less aggressive subtypes does not seem to reflect the more aggressive nature of metastatic lesions, the RT-qPCR based methods seem to be more reliable. Metastatic tissue should therefore be reevaluated with regard to markers relevant to treatment such as ESR1 and ERBB2; preferably by standardized RT-qPCR methods. Validation of these findings in an independent cohort of similar size is ongoing and will be presented at the meeting. Citation Format: Wallwiener M, Deutsch TM, Hartkopf AD, Domschke C, Taran F-A, Brucker S, Wirtz R, Trumpp A, Schneeweiss A. Gene and protein expression profiles of HER2, ER, PR, and Ki67 in matched pair samples of primary (PBC) and metastatic breast cancer (MBC) tissues. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P2-08-18.