Abstract 499: ESR1 methylation in circulating tumor cells of patients with breast cancer

Abstract

Abstract AIMS: DNA methylation is an epigenetic alteration which plays a decisive role in the regulation of signal translation processes. In our lab, we have demonstrated for the first time the epigenetic silencing of tumor and metastasis suppressor genes in CTCs through their promoter methylation. Estrogen receptor (ER) is an important prognostic biomarker and is predictive of response to endocrine therapy in breast cancer. In this study, we evaluated for the first time ESR1 methylation in CTCs of breast cancer patients. METHODS: We developed and validated a novel highly sensitive and specific qMSP assay for ESR1 methylation using commercially available DNA methylation controls and the MDA-MB-231 cell line. We further examined its performance in EpCAM-positive immune-magnetically isolated CTC fractions, followed by DNA isolation and sodium bisulfite (SB) treatment from: a) 74 operable, b) 48 metastasis- verified breast cancer patients and c) 30 healthy donors (control group). RESULTS: The developed assay is highly specific and sensitive since it can detect 0.1% methylated ESR1 sequences in the presence of 99.9% un-methylated. ESR1 was found to be methylated in 16/74 (21.6%) operable breast cancer patients, in 10/48 (20.8%) patients with verified metastasis, but only in 1/30 (3.3%) healthy donors (EpCAM-positive CTC fraction). CONCLUSIONS: The EpCAM-positive CTC fraction was found to be methylated for ESR1 in about 20% of patients with breast cancer. We will further evaluate these findings in respect to the clinical outcome of these patients, since the epigenetic silencing of ESR1 could be of important clinical significance especially for its impact on the efficacy of treatment. Citation Format: Sofia Mastoraki, Areti Strati, Maria Chimonidou, Nikos S. Malamos, Vasilis Georgoulias, Evi S. Lianidou. ESR1 methylation in circulating tumor cells of patients with breast cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 499.