Epigenetic biomarkers in esophageal cancer

The aberrant DNA methylation of tumor suppressor genes is well documented in esophageal cancer, including adenocarcinoma (EAC) and squamous cell carcinoma (ESCC) as well as in Barrett's esophagus (BE), a pre-malignant condition that is associated with chronic acid reflux. BE is a well-recognized risk factor for the development of EAC, and consequently the standard of care is for individuals with BE to be placed in endoscopic surveillance programs aimed at detecting early histologic changes that associate with an increased risk of developing EAC. Yet because the absolute risk of EAC in individuals with BE is minimal, a clinical need in the management of BE is the identification of additional risk markers that will indicate individuals who are at a significant absolute risk of EAC so that they may be subjected to more intensive surveillance. The best currently available risk marker is the degree of dysplasia in endoscopic biopsies from the esophagus; however, this marker is suboptimal for a variety of reasons. To date, there are no molecular biomarkers that have been translated to widespread clinical practice. The search for biomarkers, including hypermethylated genes, for either the diagnosis of BE, EAC, or ESCC or for risk stratification for the development of EAC in those with BE is currently an area of active research. In this review, we summarize the status of identified candidate epigenetic biomarkers for BE, EAC, and ESCC. Most of these aberrantly methylated genes have been described in the context of early detection or diagnostic markers; others might prove useful for estimating prognosis or predicting response to treatment. Finally, special attention will be paid to some of the challenges that must be overcome in order to develop clinically useful esophageal cancer biomarkers.