Epigenetics is the study of how behavioral and environmental factors can impact our genes. Epigenetic changes in DNA are not permanent and can be reversed. Epigenetic changes, including DNA methylation, can lead to colorectal cancer when normal glandular epithelium is transformed into invasive adenocarcinoma. In gastric cancer, epigenetic changes such as gene promoter region hypermethylation, genomic global hypomethylation, histone modifications, and alterations of noncoding RNAs are all associated with cancer development.