Aromatase inhibitors are the major first-line treatment of estrogen receptor-positive breast cancer, but resistance to treatment is common. To date, no biomarkers have been validated clinically to guide subsequent therapy in these patients. In this study, we mapped the genome-wide chromatin-binding profiles of estrogen receptor a (ERa), along with the epigenetic modifications H3K4me3 and H3K27me3, that are responsible for determining gene transcription (n ¼ 12). Differential binding patterns of ERa, H3K4me3, and H3K27me3 were enriched between patients with good or poor outcomes after aromatase inhibition. ERa and H3K27me3 patterns were validated in an additional independent set of breast cancer cases (n ¼ 10). We coupled these patterns to array-based proximal gene expression and progression-free survival data derived from a further independent cohort of 72 aromatase inhibitor-treated patients. Through this approach, we determined that the ERa and H3K27me3 profiles predicted the treatment outcomes for first-line aromatase inhibitors. In contrast, the H3K4me3 pattern identified was not similarly informative. The classification potential of these genes was only partially preserved in a cohort of 101 patients who received first-line tamoxifen treatment, suggesting some treatment selectivity in patient classification. Cancer Res; 73(22); 6632-41. Ó2013 AACR.

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For patients with metastatic breast cancer, we previously described that increased EZH2 expression levels were associated with an adverse outcome to tamoxifen therapy. Main objective of the present study is to investigate miR-26a and miR-101 levels, which both target EZH2, for their association with molecular pathways and with efficacy of tamoxifen as first-line monotherapy for metastatic breast cancer. Expression levels were measured using quantitative Real-Time Polymerase Chain Reaction (qRT-PCR) in primary breast cancer specimens of 235 estrogen receptor-α (ER)-positive patients. Pathway analysis was performed on microarray data available for 65 of these tumors. Logistic regression and Cox uni- and multivariate analysis were performed to relate expression levels with clinical benefit and time to progression (TTP). Increasing levels of miR-26a were significantly (P < 0.005) associated with both clinical benefit and prolonged TTP, whereas miR-101 was not. Cell cycle regulation and CCNE1 and CDC2 were the only significant overlapping pathway and genes differentially expressed between tumors with high and low levels of miR-26a and EZH2, respectively. In addition, increasing mRNA levels of CCNE1 (P < 0.05) and CDC2 (P < 0.001) were related to poor outcome. Multivariate analysis revealed miR-26a and CDC2 as an optimal set of markers associated with outcome on tamoxifen therapy, independently of traditional predictive factors. To summarize, only miR-26a levels are related with treatment outcome. Cell cycle regulation is the only overlapping pathway linked to miR-26a and EZH2 levels. Low mRNA levels of EZH2, CCNE1, and CDC2, and high levels of miR-26a are associated with favorable outcome on tamoxifen.Electronic supplementary materialThe online version of this article (doi:10.1007/s10549-011-1877-4) contains supplementary material, which is available to authorized users.

In vitro, E ZH2 silencing in MCF7 c aused a 38% decrease in cell numbers (P< 0.001) whereas ICI 164.384 treatment resulted in a 25% decrease (P<0.001) compared to controls.Combining E ZH2 silencing with ICI-treatment reduced c ell numbers with 67% (P< 0.001) compared t o control conditions. E ZH2 downregulation was associated with an almost 2-fold upregulation of the estrogen receptor alpha (E R) (P=0. 001).Conclusion: E ZH2 has no prognostic value in breast cancer. High levels of E ZH2 are associated with poor outcome to tamoxifen therapy in advanc ed breast cancer. Downregulated EZH2 leads to upregulation of the ER and better response to anti-estrogens.3