Unravelling the epigenomic dimension of breast cancers

Purpose of review Breast cancer remains the first cause of cancer-related mortality in women. This can be explained by the high histological and molecular heterogeneity of the disease, making it hard to choose a therapy adapted to each patient. Over this last year, several groups have evaluated the epigenetic component of breast cancer, as epigenetics appears to be important in carcinogenesis. Results suggest that assessing the epigenetic aspects of breast tumours could strongly improve our understanding of the biology and heterogeneity of breast cancers. Recent findings The heterogeneity of breast tumours described at the histological and transcriptional levels exists also at the epigenetic level. DNA methylation profiles both confirm previous observations based on histological and transcriptomic analyses and add new levels of complexity to the picture. Several methylation signatures have been evidenced, that can stratify patients in terms of prognosis. DNA methylation profiles could also be a marker of lineage restriction, reflecting the cell type from which a tumour originates. Summary While focusing mainly on gene promoters and CpG islands, the genome-scale DNA methylation profiling studies, conducted last year, highlighted the need to evaluate the epigenetic component in order to gain better knowledge of breast cancer biology, thereby, to improve patient management. Clearly, however, the epigenomic exploration of breast cancers has only just begun, recent studies having revealed the importance of DNA methylation in regions such as gene bodies and intergenic regions that still need to be explored.