Abstract P4-02-12: Comparison of RT-qPCR with consensus immunohistochemistry by three pathologists for ER, PR, HER2 and Ki-67 in Chinese breast cancer patients

Abstract

Abstract Background During the diagnostic work-up of breast carcinomas, immunohistochemistry (IHC) is the currently used method for assessing the expression of estrogen- (ER) and progesterone-receptors (PR), human epidermal growth factor receptor 2 (HER2) as well as of Ki-67 as a marker of tumor cell proliferation. In this study, we analyzed the concordance of these four breast cancer biomarkers between the RT-qPCR- and IHC-based (evaluated by three independent pathologists) determinations. Methods The expression of ER/ESR1, PR/PGR, HER2/ERBB2 and Ki-67/MKI67 was determined in 269 FFPE breast cancer samples with tumor content >20% from Chinese patients. For IHC, the samples were freshly cut, stained and assessed by three independent pathologists using the same scoring methods in a blinded fashion (positivity defined as: ER/PR ≥1%, HER2 >2+ and Ki-67 ≥20%). Measurement of the markers on the mRNA level was done on total RNA extracts prepared from whole tissue sections from the same FFPE blocks using the CE-marked RT-qPCR based IVD MammaTyper® on a Cobas® z480 qPCR cycler. IHC assessments of the three pathologists were compared to each other with regard to concordance of positive/negative results. Subsequently, agreement of RT-qPCR and IHC results for each marker and in samples in which the three pathologists had a consensus positive/negative IHC result was determined. Furthermore, we compared the MammaTyper® assessments from a subset of whole FFPE sections to data obtained from paired samples enriched for invasive carcinoma via macrodissection. Results From the 269 samples, 256 were available for final analysis. When excluding cases with discordant IHC callings between the three pathologists (6.0% for ER; 7.4% PR; 4.1% Her2; 17.1% Ki-67)) the concordance to the RT-qPCR determination and consensus IHC-based analysis displayed an excellent agreement for ER (OPA: 95.4%, PPA: 97.5%, NPA: 91.5%, Kappa: 0.897), PR (OPA: 91.1%, PPA: 89.6%, NPA: 93.1%, Kappa: 0.820) and HER2 (OPA: 97.1%, PPA: 91.9%, NPA: 100.0%, Kappa: 0.936). For cancer MKI67 mRNA and Ki-67 protein expression, a lower but still good concordance was found (OPA: 90.1%, PPA: 91.8%, NPA: 83.3%, Kappa: 0.707). In addition, we could demonstrate an excellent agreement of quantitative RT-qPCR measurements between whole surface and paired tumor-enriched samples in 99 Chinese breast cancer patients with R2 of 0.927 for ER, 0.926 for PR, 0.923 for HER2 and 0.908 for KI67. Even under highly standardized IHC scoring conditions, the discordance rates in the RT-qPCR marker callings with 0.0% for ESR1, 5.0% for PGR, 3.0% for ERBB2, 13.1% for MKI67 were lower than disagreements by three pathologists on the identical slide. Conclusion Standardized determination of the breast cancer biomarkers ER, PR, HER2 and Ki-67 on the mRNA level shows high concordance to a consensus IHC determined by three experienced pathologists indicating that RT-qPCR may be a valid alternative for determining the four breast cancer biomarkers. In line with previous research we could show on a large set of samples that macrodissection is not required for reliable assessment of the four breast cancer markers in clinical FFPE samples. Citation Format: Teng X, Li X, Xu S, Zhang J, Hartmann K, Laible M, Hipfel R, Bai Y, Ba X, Wu Z, Wirtz RM, Liu S, Ugur S. Comparison of RT-qPCR with consensus immunohistochemistry by three pathologists for ER, PR, HER2 and Ki-67 in Chinese breast cancer patients [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P4-02-12.