MDM2 and melanoma: Common pathways such as JAK/STAT signaling up-regulate tumor MHC-II expression, whereas, in breast cancer, RAS/MAPK signaling inhibits MHC-II expression.144, 145, 146 MDM2 is overexpressed in a variety of tumors, including melanoma,147 and plays an important role in the regulation of MHC expression in tumor cells.