CXCR4 and cancer: Chemokines are small proteins with low molecular weight and play a key role in tumor immunity and communication between tumor cells and their surrounding environment(62), such as CCR9/CCL25, CXCR5/CXCL13, CXCR4/CXCL12 and CCR7/CCL19 (CCL21), which play a role in cancer growth and metastasis.