PTK2 and melanoma: FAK, a non-receptor protein tyrosine kinase, is an important key mediator of the aggressive melanoma phenotype including VM, through Erk1/2 and unknown downstream effectors to regulate or promote invasion and migration of aggressive melanoma cells that may contribute to an increase of VM potential; moreover, Erk1/2 regulates MMP-2 and membrane type 1-MMP (MT1­MMP) activity, thus promoting melanoma invasion and VM [48], [49].