CXCL12 and neoplasm: As there is no increase in CXCR4 expression seen in the MTLn3 JP tumor cells [see Additional data file 3], the response seen in MTLn3 JP tumors to high levels of CXCL12 may reflect initiation of the paracrine loop by tumor-associated macrophages, which express CXCR4 [44-46].