Abstract
Abstract Background: Understanding the diversity of breast cancer is essential to improving diagnosis and optimising treatment. Both genetic and acquired epigenetic abnormalities participate in cancer, but information is scant on the involvement of the epigenome in breast cancer and its contribution to the complexity of the disease. Our goal was to explore the DNA methylation landscapes of phenotypically heterogeneous tumours, to relate this diversity to landscape features, and extract biological and clinical meaningful information. Methods: We performed comprehensive DNA methylation profiling to assess the methylomes of two independent sets of frozen breast tissue samples: a “main set” of 123 samples (4 normal and 119 infiltrating ductal carcinomas, IDCs), and a “validation set” of 125 samples (8 normal and 117 IDCs). We used the recently developed Illumina's Infinium Methylation Assay, that allows to assess the methylation status of more than 27,000 CpGs corresponding to over 14,000 genes. Results: Firstly, it emerged that the two major phenotypes of breast cancers determined by ER status are widely epigenetically controlled. Secondly, we have distinguished, and validated in an independent set of tumours, 6 methylation-profile-based tumour groups, some coinciding with known “expression subtypes” but also new entities that may provide a meaningful basis for refining breast tumour taxonomy. Thirdly, we showed that DNA methylation profiling can reflect the cell type composition of the tumour microenvironment. Lastly, we highlighted an unexpectedly strong epigenetic component in the regulation of key immune pathways, revealing a set of immune genes having high prognostic value in specific tumour categories. Conclusions: In this study, we have generated the largest and most comprehensive DNA methylation data set for human breast tumor tissues. Several novel findings and original concepts for breast cancer emerge, that previous RNA expression profiling has not highlighted. By laying the ground for better understanding of breast cancer heterogeneity and improved tumor taxonomy, the precise epigenetic portraits drawn in our work should contribute to better management of breast cancer patients. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-180. doi:10.1158/1538-7445.AM2011-LB-180
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