CXCR4 and pituitary tumor: In fact, CXCL12 and CXCR4 are concomitantly upregulated in hypoxic foci within pituitary tumor tissues, and one of the main CXCL12 effects in pituitary adenomas is to mobilize CD34- (and CXCR4-) expressing endothelial progenitors and promote their homing in ischemic foci activating the proangiogenic program [203].