The upregulation of miR-let-7b in the adult compared to the pediatric and young adult group is intriguing, in view of the finding of Schultz whereby forced overexpression of let-7b in melanoma cells in vitro downregulates the expression of cyclin-D1, D3, A, and cyclin dependent kinase (CDK4), all of which have been described to play a role in melanoma development [35] (Additional file 3). This evidence concerns the gene CCND1 and melanoma.