Complexity of microRNA (miRNA, also miR) regulation in melanoma. Examples of various ways that miRNAs regulate expression of gene(s) involved in cancer hallmark characteristics. A: miR-137 is an example of how a single miRNA can regulate many genes, enabling melanoma cells to acquire multiple hallmark functions (6, 53). B: micropthalmia-associated transcription factor (MITF) is an example of one gene regulated by multiple miRNAs to fine tune the control of gene expression (6, 28, 30, 78). C: ApoE signaling pathway is an example of multiple miRNAs regulating multiple genes within one signaling pathway in order to maximize inhibition of this pathway (69).