Although the CD133 cell population co-expresses other stem cell markers or may represent overlapping markers, recent reports on metastatic melanoma containing CD133 and ABCG2-positive cells with enhanced tumorigenic potential further support our present findings on consistent expression of stemness marker CD133 in conjunction with ABCB5 in various progressive stages of cutaneous melanoma (25,26). This evidence concerns the gene PROM1 and metastatic melanoma.