Abstract P2-05-25: Predictive value of ultra-high ESR1 mRNA expression in early breast cancer

Abstract

Abstract Background Quantitative determination of estrogen receptor mRNA expression in luminal breast tumors is predictive for benefit from adjuvant tamoxifen compared to placebo treatment as has been shown in the large randomized NSABP B-14 trial, while protein determination by IHC or LBA is not (Kim et al JCO 2011). Interestingly, the ultrahigh expression of ESR1 mRNA (above ER score 10 by Oncotype test) has been indicative for tamoxifen benefit. This predictive cut-off value of mRNA expression is significantly higher than the diagnostic cut-off (at ER score 6.5). Here we tested wether the ultrahigh expression of ESR1 mRNA determined by commercial MammaTyper® testing is predictive for survival after neoadjuvant chemotherapy treatment of advanced breast cancer. Materials and Methods Pretreatment core cut biopsies from n=54 patients with PBC treated within a randomized phase II trial (2) of anthracyline/taxane based NAC with available clinical follow-up information were examined. RNA was extracted from the FFPE sections and ESR1 mRNA from each section was measured by commercial assays. For technical comparison of ESR1 mRNA values by Oncotype DX versus MammaTyper® from n=113 surgical samples were analyzed by both commercial assays in a blinded fashion. Statistical analysis was performed using the SAS JMP® 9.0.0 software. Results Quantification of ESR1 mRNA expression after RNA extraction from separate slices of 113 primary breast tumors and determination by different commercial RT-qPCR assays resulted in high correlation of continuous expression results (Spearman r=0,85; p<0,0001). The rate of ESR1 mRNA negative cases by both methods by predefined diagnostic cut-offs was low in this cohort (1/113 and 6/113, respectively) resulting in high concordance for positive ER status by both methods.The median expression of ER score and ESR1 40-DDCq was high (10,2 and 39,8, respectively) and almost exactly at the predictive ER score cut-off. Hence, the Tamoxifen benefit cut-off of ER score 10 by Oncotype is comparable with a 40-DDCqvalue of 39,6 for ESR1 mRNA determination by MammaTyper®, which resembles an ESR1 mRNA expression 3fold above the diagnostic cut-off. In the independent chemotherapy cohort theoptimal discrimination for overall survival could be achieved by an elevated ESR1 mRNA expression exactly at 39,6 resulting in 100% overall survival for ultra-high expressors and 75 % overall survival for lower ESR1 mRNA expression after 5 years (p=0,006). Conclusion Previous data suggest that ultrahigh expression of ESR1 mRNA is predictive for improved overall survival and tamoxifen benefit (1). Here we show that ultrahigh expression of ESR1 mRNA is also prognostic in more advanced breast tumors after neoadjuvant chemotherapy. These findings validate the importance of quantitative determination of estrogen receptor expression and substantiate the understanding of receptor expression being a continuous determinant with indication specific cut-off values. Ultrahigh expression of ESR1 seems to identify a distinct subset of luminal breast tumors with superior prognosis and benefit from tamoxifen treatment. These findings warrant further investigation, which are currently being done in independent large breast cancer cohorts. Citation Format: Wirtz RM, Scheffen I, Marme F, Laible M, Sclombs K, Schumacher C, Schneeweiss A, Eidt S, Sinn H-P. Predictive value of ultra-high ESR1 mRNA expression in early breast cancer [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P2-05-25.