CXCL12 and neoplasm: A key role of chemokine CXCL12 and its receptors is in regulating metastasis by multiple mechanisms including facilitating tumor spread, affecting endothelial adhesion, eruption from blood vessels, proliferation, angiogenesis, colonization, and evasion from host response via activation of key survival pathways regulated by ERK/MAPK, Jak/STAT, and PI3K/Akt/mTOR signaling [39].