CXCR4 and neoplasm: For instance, the primary and most significant chemotactic factor secreted by CAFs is CXCL12 (or stromal cell-derived factor-1, SDF-1), which recruits CXCR4-expressing immunosuppressive Tregs and endothelial progenitor cells, thus participating in tumor angiogenesis, proliferation, and immunosuppression via the CXCL12/CXCR4 axis [65,72,73].