CXCR4 and neoplasm: Importantly, the tumor cells could significantly produce not only the ILs such as IL-6, IL-8, and IL-11, required for osteoclastogenesis [127], but also strengthen the expression of CXCR4 and CXCR7, establishing a “fertile soil” that accelerates tumor cells to adhere to bone matrix and thrive in bone [128, 129] (Figure 1).