Despite the recent introduction of advanced microarray-based gene expression profiling strategies, relapse risk assessment and individual treatment recommendations remain suboptimal for breast cancer patients. DNA methylation emerges as a novel source of epigenetic biomarkers that can help improve individualised breast cancer therapy. In the light of existing preclinical and clinical data we studied NT5E (5′-nucleotidase, ecto) expression and NT5E promoter methylation (NPM) in 14 breast cancer cell lines and 259 breast cancer clinical cases. In vitro, NT5E promoter methylation (as determined by MSP and pyrosequencing) was inversely associated with NT5E expression (as determined by qRT-PCR) and azacytidine produced an increase in NT5E mRNA levels in cell lines with methylated the NT5E promoter CpG. In clinical series, patients whose resected primary tumours were found to have NT5E promoter methylation, were less likely to develop metastasis (p=0.003, OR=0.34, 95% CI 0.17-0.69). Moreover in 3 out of 4 paired samples, NT5E promoter was found methylated in primary tumours and demethylated in CNS metastases. Regarding metastatic profile, patients that progressed to non-visceral metastases were more likely to have NT5E promoter methylated in primary tumours as compared to visceral metastatic disease (p=0.01, OR=11.8). NT5E promoter CpG island was densely methylated in 16 of 21 patients who developed non-visceral metastatic disease (76%) and in 6/28 cases (21%) with visceral metastases. In time-dependent endpoints analysis, patients with tumours lacking detectable NT5E methylation had increased risk for shorter DFS (p=0.001, HR 2.7) and OS (p=0.001, HR=3). The favourable prognostic value of NT5E methylation was confirmed in ER negative (p=0.011, HR=3.27, 95% CI 1.31-8.12) and in triple negative cases (p=0.004; HR=6.2, 95% CI 1.9-20). Moreover we observed a strikingly favourable outcome to adjuvant chemotherapy in patients with tumours profiled as NT5E promoter methylated regarding DFS (p=0.0016, HR 5.1, 95% CI 1.8-14.37) and OS (p=0.0005, HR 7.4, 95% CI 2.416 –23.08), which allows speculations that NPM may convey breast cancers more amenable to chemotherapy, possibly though pro-apoptotic mechanism. We suggest that NT5E promoter CpG island methylation may serve as a promising favourable breast cancer epigenetic biomarker. Our results warrant independent confirmation by other groups before considering its investigation as a metastasis predictor in clinical trials of adjuvant breast cancer therapies.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4550. doi:1538-7445.AM2012-4550