While the term epigenetics is often used loosely, and sometimes in rather different ways, the term is generally considered to encompass changes in DNA methylation, histone modifications, miRNA expression, and nucleo-some positioning and higher order chromatin as epigenetic changes affecting gene regulation. Epigenetics was defined as a discipline more than 50 years ago, by CH Waddington, and originally described changes in the development of organisms that could not be explained by changes in DNA. Subsequently it became clear that epigenetic modifications play important roles in diseases, including breast cancer. There is thus a pressing need to understand the functional genome; that is, the changes defined by regulatory mechanisms overlaying the genetic structure. Over the past few years there has been an explosion in studies of epigenetics in breast cancer, reflected by the exponential increase of published manuscripts. A PubMed search for the keywords epigenetic and breast cancer reveals that the first publication was in 1983. Progress was slow until approximately 10 years ago when the number of studies started to steadily increase, at least in part fueled by improved technologies. In the present review, we focus on recent advances in the understanding of histone methylation and demethylation, a relatively new area with promise for clinical translation. We also review recent studies that have utilized genome-wide technologies for the study of DNA methylation. Much progress has been made in the characterization of noncoding RNAs, and the effect of higher order chromatin structure on gene expression in breast cancer; however, these discoveries lie outside the scope of our review. Breast Cancer Res. 2011; 13(6): 225. De acordo com o texto acima, epigenética é uma