Cancer cells secrete a variety of cytokines and chemokines to recruit monocytes to the tumor side, including IL-6, IL-8, IL-34, CCL2, CCL3, CCL5, CCL20, CSF-1, CSF-2 and C-X-C motif chemokine 12 (CXCL12). Here, CXCL12 is linked to cancer.