Causes, effects, and clinical implications of perturbed patterns within the cancer epigenome

Somatic mutations accumulating over a patient's lifetime are well-defined causative factors that fuel carcinogenesis. It is now clear, however, that epigenomic signature is also largely perturbed in many malignancies. These alterations support the transcriptional program crucial for the acquisition and maintenance of cancer hallmarks. Epigenetic instability may arise due to the genetic mutations or transcriptional deregulation of the proteins implicated in epigenetic signaling. Moreover, external stimulation and physiological aging may also participate in this phenomenon. The epigenomic signature is frequently associated with a cell of origin, as well as with tumor stage and differentiation, which all reflect its high heterogeneity across and within various tumors. Here, we will overview the current understanding of the causes and effects of the altered and heterogeneous epigenomic landscape in cancer. We will focus mainly on DNA methylation and post-translational histone modifications as the key regulatory epigenetic signaling marks. In addition, we will describe how this knowledge is translated into the clinic. We will particularly concentrate on the applicability of epigenetic alterations as biomarkers for improved diagnosis, prognosis, and prediction. Finally, we will also review current developments regarding epi-drug usage in clinical and experimental settings.