This review summarizes the epigenetic mechanisms of deoxyribonucleic acid (DNA) methylation, histone modifications in cancer and the epigenetic modifications in cancer therapy. Due to their undesired side effects, the use of epigenetic drugs as chemo-drugs in cancer therapies is limited. The drug delivery system opens a door for minimizing these side effects and achieving greater therapeutic benefits. The limitations of current epigenetic therapies in clinical cancer treatment and the advantages of using drug delivery systems for epigenetic agents are also discussed. Combining drug delivery systems with epigenetic therapy is a promising approach to reaching a high therapeutic index and minimizing the side effects.