In a Ni-induced muscle tumor model in Wistar rats, the mRNA expressions of retinoic acid receptor beta (RAR-β2), Ras association domain family member 1 (RASSF1A), and cyclin-dependent kinase inhibitor 2A (CDKN2A) were decreased, and hypermethylation of the 5’ region of these genes was found in the muscle tumors [103]. This evidence concerns the gene CDKN2A and myomatous neoplasm.