CXCR4 and neoplasm: Autocrine activation, occurring as a result of the interaction between CXCR4 and CXCL12 expressed by tumour cells, promotes proliferation and invasion, whereas paracrine signalling, occurring due to the interaction between CXCR4 on tumour cells and CXCL12 on microenvironmental stromal cells, promotes tumour proliferation and metastasis to secondary sites.13