In addition, genes that are frequently subject to epigenetic inactivation in human cancers, such as Ras association domain-containing protein 1 (RASSF1A) [52] and hypermethylated in cancer 1 protein (HIC1) [53], are also frequently hypermethylated in parathyroid adenomas, but it is unclear which of these aberrantly methylated genes may be important to the pathogenesis of parathyroid tumors. Here, HIC1 is linked to tumor of parathyroid gland.