Nerve resident macrophages accumulate in the nerves invaded by tumor cells by following the gradient of CCL2 and CSF-1 recognized by CCR2 and CSF-1R receptors, respectively; CSF-1 receptor blocker (GW2580) prevents the migration of endoneurial macrophages induced by tumor-derived factors.195 Then, tumor cell migration is triggered by RET receptors activated by GDNF released by activated macrophages (Fig. 4). This evidence concerns the gene GDNF and neoplasm.