P1-05-03: Relationship between Polycomb Repressive Complex EZH2/CBX7, Large Non-Coding RNA ANRIL and Stem Cells Biomarkers in Triple Negative Breast Carcinomas: Important Role in Carcinogenesis through an Epigenetic Silencing Process and New Clues for Targeted Therapies.

Abstract Background: Epigenetic deregulation and carcinogenesis are intimately connected and gene silencing is a major consequence of epigenetic modifications. Polycomb group proteins (PcG) play important roles by inhibiting chromatin remodeling and transcription, silencing tumor suppressor genes, regulating stem cells and interconnecting with Wnt/beta-catenin, TGF-beta and Sonic-Hedgehog pathways. EZH2 is a transcriptional repressor and acts mainly as an oncogenic silencer gene involved in cell cycle regulation. Large non coding RNA are major regulators of oncogenic and oncosuppressive pathways at epigenetic, transcriptional and post-transcriptional levels. Recent studies have showed that (i) EZH2 overexpression is associated with cancer progression and aquisition of stem cell properties and (ii) disruption of ANRIL/CBX7 interactions repress the INK4b/ARF/INK4a locus. The aim of the study was to analyze PRC complexes, large non-coding RNA ANRIL and downstream signaling targets in triple negative breast carcinomas (TNC). Design: By using real time quantitative RT-PCR in a series of 432 invasive breast ductal carcinomas (IDC), we quantified gene expression levels of the large non coding RNA ANRIL, PcG (EZH2, CBX7, SUZ12), stem cells markers (ALDH1, CD133, ASCL1) and oncosuppressor genes (p15, p16 and p19). Immunohistochemistry (IHC) was performed using EZH2, CBX7, ALDH1 and b-catenin Abs. We compared mRNA expression levels and IHC intensity score in TNC with non TNC and normal breast parenchyma. Results: EZH2 overexpression was respectively found by RT-PCR and IHC in the TNC subgroup of IDC. We observed variable mRNA expression levels of SUZ12, CBX7, ANRIL, ALDH1, CD133, ASCL1, p15, p16, and p19. IHC showed EZH2 and CBX7 nuclear staining. Mutual positive correlations were found between EZH2, CBX7, ALDH1, ASCL1 and CCND1 (p&amp;lt;10-5). Conclusion: Polycomb EZH2/CBX7 and the large non coding RNA ANRIL are epigenetic transcriptional repressors overexpressed in the TNC subgroup of IDC. Their implication in the process of gene silencing (p16, p15, p19), activation of oncogenic pathways (Wnt, TGFb) and tumor stem cells self-renewal may explain several hallmarks of TNC and open new avenues to target this aggressive subgroup. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P1-05-03.</jats:p

DNA repair gene expression profile and risk of locoregional relapse in locally advanced breast cancer patients

528 Background: The cytotoxicity of radiation therapy appears mainly mediated through the induction of DNA-double strand breaks. We explore whether DNA repair gene expression could be associated with the risk of locoregional recurrence (LRR) in locally advanced breast cancer patients. Methods: mRNA levels of 21 selected DNA repair genes were measured in tumors samples of 97 locally advanced breast cancer patients included in a phase III trial (CRH cohort), using quantitative reverse-transcriptase polymerase chain reaction. Normalized mRNA levels were evaluated for association with LRR-free survival (LRR-FS) and overall survival (OS). Results were validated in an independant cohort (Netherlands Cancer Institute: NKI cohort). Multivariate analysis, including known prognostic factors, was done to assess the association between gene expression profile of DNA repair genes and outcomes. Results: Overexpression of RAD51, PRKDC, and XRCC6 were associated with a higher risk of LRR in the CRH cohort. RAD51 was the only gene associated with LRR in the NKI cohort. With a median follow-up of 126 months (CRH cohort), the 5-year LRR-FS rates were 100% in patients (n = 61) with low RAD51, compared with 70% in patients (n = 36) with high RAD51 (p &lt; 0.0001). The 5-year OS rates were 95% in patients with low RAD51, compared with 69% in patients with high RAD51 (p = 0.00026). RAD51 overexpression was associated with a higher risk of LRR (multiadjusted hazards ratio [HR], 12.83, 95% CI: 3.6 - 45.6) and a higher risk of death (multiadjusted hazards ratio [HR], 4.10, 95% CI: 1.7 - 9.7). RAD51 was also significantly associated with shorter LRR-FS and OS in the NKI cohort. Conclusions: Our results suggest that overexpression of RAD51, a key component of the homologous recombination and the DNA DSBs repair, is associated with a higher risk of LRR and death, and may be a prognostic marker of LRR in locally advanced breast cancer patients. No significant financial relationships to disclose. </jats:p