MMP21 and melanoma: Among several hundred citrullinated proteins [52], α-enolase (ENO1), vimentin (VIM), nucleophosmin (NPM1), matrix metalloproteinase-21 (MMP21), cytochrome p450 (Cp450), and glutamate receptor ionotropic (GRI) citrullinated peptides have been selected for immunization for melanoma, lung, pancreas, and ovarian cancers [29,30,33,53,54,55].