CCL2 and bone cancer: Recent studies have reported that, in bone cancer, chemokines and their receptors, such as CXCL12/CXCR4 [22], CCL2 [35], and CXCR3 [36], mediate the activation of microglia and astrocytes in the SDH via intracellular signals including MAPKs and NF-κB pathways, consistent with our results that MAPK pathways were activated in the SDH by bone cancer.