Abstract P3-06-45: Concordance/discordance rates of HER2, ER, PR, and Ki67 in matched pair samples of primary (PBC) and metastatic breast cancer (MBC) tissues when comparing IHC with MammaTyper® RT-PCR kit
2015-05-01

Abstract Background Clinical decisions in the primary and advanced situation of breast cancer are based on immunohistochemical staining (IHC) and semiquantitative assessment of ER, PgR, HER2 and Ki67. However, IHC carries an up to 20% risk of erroneous results. Moreover, metaanalysis revealed variable discordance rates between primary and metastatic sites (P/M) which may have implications for patient management (Aurilio, Eu J Cancer 2013). Herein, we undertook a pilot study aiming to investigate whether the reported discordance between primary lesion and paired distant metastatic sites is due to technical limitations of the IHC technique and could be improved by mRNA analysis using the MammaTyper® in vitro diagnostic assay. Materials and Methods One 10μm-thick sections from clinical routine FFPE tissues of 28 tumor samples were reexamined by RNA quantitation of ESR1, PGR, HER2 and KI67 using the RNXtract® kit for RNA extraction and MammaTyper® kit for objective assessment of receptor status. RNA levels were normalized using a synthetic in-vitro transcript for normalization according to the 40-DDCT method. Receptor status was reported based on predefined cut-offs according to the instruction for use. mRNA and IHC results were compared between paired primary and metastatic sites. Results Concordance per tumor sample between the two methods was 100% for HER2, 81.9% for ESR1 and 81.5% for PR. Among discrepant samples (N=8), 6 were primary and among these, half (N=3) were due to negative ER by IHC. With the exception of HER2, where no differences were observed for either method, the P/M concordance was superior by MammaTyper® kit (ESR1: 92.85 vs. 76.82, PR: 71.43 vs. 69.23). Importantly, several discordant cases by IHC were ER negative in the primary site, while being ER positive in the metastatic lesion, while being consistently ESR1 positive in both sites, when determined by the more sensitive PCR method. The subtype discordant cases were situated in the lung (2), the liver (1) and the bone marrow (1). Conclusion Our data indicate that receptor status shifts less frequently when determined by PCR methods compared to IHC. While some shifts between primary site and metastases may arise from true progression-related biologic alterations (Prat et al Nat Med 2009), others seem to be related to technical limitations of semiquantitative and subjective IHC, with several cases being conspicuous for ESR1. This finding is of great clinical significance and is consistent with previous reports implicating technical confounders of IHC for large part of the observed P/M deviations (Pusztai, The Oncologist 2010). The implied superiority of RT-qPCR by MammaTyper® vs. routine IHC in detecting true P/M tumor receptor status reversals and the possible clinical impact is clearly worth pursuing in larger datasets. Citation Format: Markus Wallwiener, Andreas Hartkopf, Thomas Deutsch, Lakis Sotiris, Florin-Andrei Taran, Andreas Trumpp, Ralph Wirtz, Andreas Schneeweiss. Concordance/discordance rates of HER2, ER, PR, and Ki67 in matched pair samples of primary (PBC) and metastatic breast cancer (MBC) tissues when comparing IHC with MammaTyper® RT-PCR kit [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 P3-06-45.