Epigenetic modifiers (e.g., Smarca4, PBRM1, ARID1A, ARID2, ARID1B, DNMT3A, TET2, MLL1/2/3, NSD1/2, SETD2, EZH2, and BRD4) modify the epigenome directly through DNA methylation, the post-translational modification of histones, or the alteration of the structure of chromatin, and they are frequently subjected to mutations in cancer. The gene discussed is TET2; the disease is cancer.