Abstract 679: Retrospective evaluation of the BRCA1 - PARP pathway in breast cancer tissues
Authors: Jacot William , Thezenas Simon , Lopez-Crapez Evelyne , Bibeau Frédéric , Bleuse Jean-Pierre , Romieu Gilles , Lamy Pierre-Jean 
Published: August 2012

Purpose: Poly(adenosine diphosphate-ribose) polymerase (PARP) and BRCA1 plays a key role in DNA repair and cellular stress response. Inhibitors of PARP show promising clinical activity in metastatic, triple-negative or BRCA-mutated breast cancer. However, a comprehensive analysis of the PARP activity / BRCA1 methylation profile in non-BRCA1 mutated tumors has not yet been assessed. Methods: We investigated cytosolic PARP activity and BRCA1 methylation profile in 155 surgical tumour samples from patients treated in our institution between January 2006 and November 2009 and evaluated their statistical association with classical breast cancer predictive and prognostic factors. DNA methylation patterns in the CpG islands of BRCA1 gene promoter were determined by a methylation specific PCR distinguishing unmethylated from methylated alleles in a given gene on the basis of sequence changes produced following bisulfite treatment of DNA. Cytosolic PARP activity was evaluated using a commercially available assay kit. Results: A total of 155 BC patients (50 HER-2 positive, 57 hormone receptors positive (HR+) / HER-2 negative and 48 triple negative tumors) were considered eligible for this study. Median age was 54 years (range 29-75 years). Only one tumor was classified as SBR score I and SBR Tubule formation score 1. No tumor was SBR Nuclear pleomorphism score 1. Considering these results, SBR scores I and II and SBR Tubule formation scores 1 and 2 were grouped for statistical analyses. Mean PARP activity (U/mg of cytosolic protein) was 12.2 (standard deviation 17.02), with a median of 7.0 (range 1.0 to 114.2). The only clearly associated parameter was SBR Mitotic count score. Bisulfite treatment was successfully performed for the whole 155 specimen. Eighteen tumors presented an hypermethylation of the BRCA1 gene promoter. The hypermethylation status was significantly associated with UPA and PAI-1 levels, SBR grade, SBR Mitotic count score, ER, PR and HER-2 negative status, and then conversely triple negative (ER, PR and HER-2 negative) profile. Twenty nine percent of the triple negative tumors presented and hypermethylated status, comparing to 5 and 2% for HR+/HER-2- and HER-2+ tumors respectively. No statistical association was found between a hypermethylation status and the PARP cytosolic activity. Conclusion: Cytosolic PARP activity is equally represented in TN, HER2+ and SBR II and III HR+ breast cancers. The only parameter clearly associated with the cytosolic PARP activity was the SBR Mitotic count score. In contrast, hypermethylation of the BRCA1 gene promoter appears restricted to a subgroup of TN tumors expressing an aggressive phenotype. No statistical association was found between a hypermethylation status and the PARP cytosolic activity. These results could allow a more accurate stratification of patients without BRCA1 famillial mutation in the future PARP inhibitors clinical trials.

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 679. doi:1538-7445.AM2012-679