CCR4 and melanoma: Moreover, brain-derived soluble factors were able to upregulate the expression of CCR3 and CCR4 in melanoma cells and enhanced the transmigration of melanoma cells through a monolayer of cerebral microvascular endothelial cells [98], further indicating that the brain microenvironment is not only important for the growth of already formed brain metastases, but also for the transmigration of melanoma cells through the BBB.