BMP2 and osteosarcoma: Hypoxia and interstitial acidosis are also important in the promotion of osteosarcoma bone metastasis, in part through activation of IL-8, IL-6, NF-κB1, colony-stimulating factors CSF2 and CSF3, BMP-2, CCL5, CXCL5 and CXCL1 in tumor-associated MSCs [156] (Figure 1).