CXCL12 and neoplasm: These findings, together with the high levels of CXCL12 in the tumor associated with a lower risk of metastasis and progression, suggest that in the primary tumor, CXCL12 endogenously produced by the tumor cells might act in a paracrine manner to contain tumor progression, making tumor cells less sensitive to the CXCL12 gradient that drives the metastatic process.