GDF15 and melanoma: The communication between metastatic melanoma cells and microglia may influence the secretion of factors that promote vascularization, such as angioprotein-2 (ANG2), by melanoma cells, and of growth differentiation factor 15 (GDF-15, also called macrophage inhibitory cytokine-1, MIC-1) and other pro-inflammatory cytokines by microglia.