Epigenetics are dynamic and inherited changes in the genome that occur independently of DNA sequencing. This phenomenon requires coherent interaction with various enzymes and other molecular components. Abnormal epigenetic changes can lead to the onset of improper gene expression and the promotion of tumorigenesis. Because epigenetic changes are prone to external and reversible factors, they are becoming promising targets in the treatment of multiple cancers. Recently, various epigenetic drugs have been developed and are involved in clinical use. The use of epigenetic drugs alone or in combination with chemotherapy or immunotherapy has shown convincing results, including increased antitumor effects, overcoming drug resistance, and activation of the host immune response.