Cancer is a disease characterized by deregulation of cellular functions. The means by which these changes occur may differ among cancer types. However, common to all cancers are that they have changed the genetic programs that determine their characteristics. Genetic programs are mainly regulated by the action of transcription factors. Changes in transcription factor activity and modification of promoter functions are therefore important changes in the development of cancer. It is also well established that DNA modulation by methylation affects the accessibility of transcription factors and that this may inhibit gene activity. Recently it has been shown that small RNA molecules called "MicroRNAs" with an approximate size of 20bp that have function in analogy to transcription factors. MicroRNAs do, however, not bind to the promoter but to the mRNA and thereby inhibit translation or induce mRNA degradation, in both cases resulting in down regulation of gene activity.