CCL13 and cancer: As a seven-transmembrane G protein-coupled receptor, CCR5 can bind to a variety of ligands CCL3 (MIP1α), CCL3L1, CCL4 (MP-1β), CCL5 (RANTES), CCL8 (MCP2), CCL11 (Eotaxin), CCL13 (MCP-4), and CCL16, which are reported to be highly expressed in most malignant tumors [9].