MC1R and metastatic melanoma: Another proteomic study shows significant increase of CEACAM1 (carcinoembryonic antigen-related cell adhesion molecule 1), MC1R (melanocortin 1 receptor), AKT1 (protein kinase B) and MMP3-9 (matrix metalloproteinases 3 and 9) and decrease in CDKN2A (cyclin-dependent kinase inhibitor 2A), SDC1 and SDC4 (syndecan 1 and 4) protein levels in distant organ metastatic melanomas [34].