Comparison of an automated cartridge-based system for mRNA assessment with central immunohistochemistry in the neoadjuvant GeparX trial.

Abstract

3075 Background: Hormone receptors, HER2 and Ki-67 are prognostic values typically determined for breast cancer (BC) outcome and prediction of therapy response. A RT-qPCR based system, the Xpert Breast Cancer STRAT4, can be used to classify BC tissues regarding their hormone receptor status, HER2 and proliferation via Ki-67. We compared mRNA expression analysis of ER, PR, HER2, and Ki-67 by this automated in-vitro diagnostic platform (GeneXpert) (GX) with central immunohistochemistry (IHC) in a large clinical trial cohort. Methods: BC patients from the prospective GBG neoadjuvant trial GeparX (NCT02682693) (still recruiting) were included in this biomarker project. We used formalin-fixed paraffin embedded (FFPE) pretherapeutical core biopsies with a tumor content > 10%. One 4 µm FFPE tissue section was first processed with the Xpert FFPE Lysis Kit, the sample lysate was placed in the STRAT4 cartridge system and then tested on the GX system in which the purification, amplification and real-time detection took place within two hours automatically. Results: A total of 503 (99%) of the 509 samples had a valid measurement of all four genes. 258 samples (51.3%) of the cohort were classified in central pathology as ER positive, 196 (39%) as PR positive and 78 (15.5%) as HER2-positive, and 421 samples (83.7%) were Ki-67-high ( > 20%). The simple kappa coefficient was for ER = 0.7938, PR = 0.6540, HER2 = 0.8172 and Ki-67 = 0.3655. This indicates, that the measurements for ER, PR and HER2 showed a high correlation between both methods, whereas the measurement of Ki-67 does not. The accuracy between the STRAT4 and IHC was 89.7% for ER, 83.3% for PR, 94.6% for HER2 and 86.7% for Ki-67. According to molecular subgroups, highest accuracy regarding Ki-67, was determined in TNBC (96.2%; luminal: 81.1%; HER2-positive: 76.9%). Conclusions: Our results show a high concordance between standardized central IHC and automated mRNA expression analysis for the most important BC biomarkers ER, PR and HER2. For the proliferation marker Ki-67, the concordance is slightly lower. The STRAT4 assay might offer additional option to conventional methods for BC biomarker assessment, in particular in settings where IHC is not feasible. To determine the clinical validity, additional outcome analyses are necessary. Clinical trial information: NCT02682693.