TET1 and melanoma: Compared with surrounding normal tissues, 5-hmC is significantly reduced in human breast, liver, lung, pancreatic, and prostate cancers with reduced expression of TET family proteins.89 Deficiency of TET1 in prostate and breast cancer is associated with tumor cell invasion and breast xenograft tumor formation via the inhibition of the methylation of metalloproteinase (TIMP) family proteins 2 and 3.90 Loss of 5-hmC is an epigenetic hallmark of melanoma, and thus, introducing TET2 into melanoma cells results in suppression of tumor growth and increased survival in an animal model91 (Table 1).