CXCL12 and chondrosarcoma: Notably, both CXCR4 and CXCL12 expression was increased in human chondrosarcoma tissues [77] and CXCR4 expression was also enhanced by hypoxia induced HIF-1α and VEGF-A expression in chondrosarcoma cell lines concomitantly with MMP1 expression [78,79,80], whereas CXCL12 induced VEGF-A secretion under hypoxic conditions [80], indicating a self-reinforcing system.