CXCL12 and colorectal carcinoma: Recent review articles related to C-X-C motif chemokine ligand 12 (CXCL12)-chemokine receptor type 4 (CXCR4)/ chemokine receptor type 7 (CXCR7) axis are focused on cancers in general, however, our focus in this review is to summarize the role of this axis in CRC progression and metastasis.