CXCL12 and cancer: Chemokines secreted by TAMs, including CCL3, CCL5, CCL15, CCL18, CXCL8 and CXCL12, promote tumor metastasis, angiogenesis, cancer cell survival, immunosuppression and resistance of cancer cells after chemotherapy via CCR1/5, CCR5, CCR1, CCR8, CXCR1/CXCR2, CXCR4, respectively.