Abstract P2-08-22: Correlation of ER (ESR1), PR (PGR), and HER2 (ERBB2) at protein and mRNA levels in operable breast cancer

Abstract Background:. We aimed to analyze the concordance between ER (ESR1), PR (PGR), and HER2 (ERBB2) levels and breast cancer subtyping results obtained by using the immunohistochemistry (IHC) and reverse transcriptase-polymerase chain reaction (RT-PCR) methods and to assess recurrence-free survival (RFS) between subtypes as determined by the two methods. Patients and Methods:. We included a total of 441 operable breast cancer patients, consisting of the training (n = 116), testing (n = 56) and validation (n = 269) cohorts in this study. Protein levels of estrogen receptor (ER) and progesterone receptor (PR) were obtained by using the IHC and that of human epidermal growth factor receptor 2 (HER2) by the IHC/FISH methods. Expression (mRNA) levels of the corresponding genes, ESR1, PGR, and ERBB2, respectively, were determined by the RT-PCR method. We then compared the status of ER (ESR1), PR (PGR), and HER2 (ERBB2) in the training, testing and validation cohorts. We categorized all validation cases into luminal (ER/PR-positive and HER2-negative), HER2 (HER2-positive regardless of ER/PR status), and triple negative (TN: ER-, PR-, and HER2-negative) subtypes accordingly. The concordance of the two methods and RFS estimated by the Kaplan-Meier methods of the three different subtypes were revealed to evaluate the clinical performance. Results:. The concordance rates between the two methods in the validation cohort were 95.1% (Kappa = 0.74) for ER (ESR1), 91.1% (Kappa = 0.67) for PR (PGR), and 93.6% (Kappa = 0.59) for HER2 (ERBB2). Kappa statistic was 0.66 for the resulting luminal, HER2 and TN subtypes. The 5-year RFS was 83.3% for luminal vs. 73.9% for HER2 vs. 48.4% for TN subtypes as determined by the IHC (p = 0.019), and 84.3% vs. 66.3% vs. 54.4% by the RT-PCR method (p = 0.016). Conclusions:. Whereas discordance existed for some cases between the IHC and RT-PCR methods for determination of the ER (ESR1), PR (PGR), and HER2 (ERBB2) status and the resulting subtypes; both the methods showed values in RFS prognosis of the population studied. It is arguable that supplementing the conventional IHC with the molecular method for subtyping of breast cancer may have beneficial clinical implications. Citation Format: Lei Lei, Xiaojia Wang, Skye Hung-Chun Cheng. Correlation of ER (ESR1), PR (PGR), and HER2 (ERBB2) at protein and mRNA levels in operable breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P2-08-22.