CX3CR1 expression is mainly restricted to microglia, whereas CX3CL1 expression is mostly confined to neurons, and co-expression of CX3CR1 and CX3CL1 promotes microglia aggregation and increased tumor microvessel density through the mediation of CCL2 and matrix metallopeptidase 9 (MMP9) upregulation, contributing to tumor progression and shifting LGG’s to a higher malignant grade (115). This evidence concerns the gene MMP9 and neoplasm.