Abstract P3-08-14: Prediction of distant recurrence in low risk early breast cancer by RT-qPCR based subtyping using MammaTyper®

Abstract

Abstract Background: Estrogen receptor (ER/ESR1), progesterone receptor (PR/PGR) and epidermal growth factor receptor 2 (HER2/ERBB2) are routinely assessed by immunohistochemistry (IHC) during workup of breast cancer samples. The routine use of Ki67 (MKI67) IHC assessment in the context of breast cancer subtyping, however, remains controversial, due to poor reproducibility and lack of standardization. The MammaTyper® test is an in-vitro diagnostic (IVD) test which measures the expression status of the four breast cancer biomarkers ERBB2, ESR1, PGR and MKI67 on the mRNA level via reverse transcription-quantitative PCR (RT-qPCR) and has demonstrated a high degree of reproducibility in the assessment of the four markers. In this retrospective analysis we assessed the prognostic power of molecular subtyping by MammaTyper® in archived samples from low risk early breast cancers treated with adjuvant endocrine therapy only. Methods: ER+/HER2- (according to initial diagnosis) FFPE breast cancer samples from patients treated with adjuvant endocrine therapy only were obtained from 6 different centers. Tumor cellularity was assessed by H&E staining and RNA was extracted from samples with a tumor cell content of ≥20% using a bead-based RNA purification kit (RNXtract®). Total RNA was then used as input for MammaTyper® RT-qPCR. Expression values were classified as positive or negative for each marker based on predefined cutoff values. Tumor subtypes were assigned to each sample based on the combination of binary (pos/neg) single marker expression status according the St Gallen surrogate subtype definition. Distant disease free survival of Luminal A-like samples vs. samples with other subtypes was assessed by Kaplan Meier analysis and Cox regression using SAS version 9.4. Results: The final analysis included 319 samples with sufficient tumor cellularity and RNA content for reliable analysis. The rate of distant recurrence in the analyzed set was 8.5%. Median follow up was 7.8 years. The MammaTyper® test called 60% (192) of samples as Luminal-A-like (4.7% (9) distant events), 37% (119) as Luminal B-like (HER2 negative) (13.4% (16) distant events), 1.3% (4) as Triple negative (ductal) (25% (1) distant events), 0.6% (2) as “not defined according to St Gallen” (ESR1-/PGR+) (50% (1) distant events) and 0.6% (2) as Luminal B-like (HER2 positive) (no distant events). When comparing Luminal A-like samples with the samples of the other subtypes in survival analysis, Luminal A-like samples had a significantly better distant disease free survival when assessing samples from patients with pN0 status (278) (p=0.0177, HR=0.344 (95% CI 0.137-0.866), pN1 status (0-3 affected nodes) (314) (p=0.0153, HR=0.374 (95% CI 0.163-0.855) as well as for all samples (p=0.0032, HR=0.319 (95% CI 0.143-0.711). Conclusion: Determination of HER2, ER, PR and Ki67 mRNA levels allows molecular subtyping according to the St Gallen surrogate subtype definition. Low risk of distant recurrence could be confirmed for the MammaTyper® Luminal A-like samples suggesting that for this patient group endocrine treatment alone may be sufficient. The high degree of standardization of mRNA measurement may drive the use of the Ki67/MKI67 biomarker in routine breast cancer pathology. Citation Format: Laible M, Hartmann K, Gürtler C, Anzeneder T, Weber S, Keller T, Sahin U. Prediction of distant recurrence in low risk early breast cancer by RT-qPCR based subtyping using MammaTyper® [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P3-08-14.