CDK4 and melanoma: In both human and mouse models of melanoma, activation of the CDK4 pathway potently cooperates with mutant BRAF or NRAS in transformation of melanocytes and RAS/RAF/MEK/ERK pathway is dysregulated in 65% to 90% of metastatic melanoma, further enhancing CDK4 pathway signaling through increasing cyclin D1 expression [175,244].