CXCR4 and neoplasm: Proximity Ligation Assays (PLA) indicate that CXCR4 and CD47 physically interact on the surface of tumor cells; the binding of CXCL12 to CXCR4 leads to the co-internalization of the CXCR4-CD47 complexes, and therefore to the decrease of surface CD47 (Figure 2).