CXCR4 and neoplasm: However, despite the antitumor effect, it is noteworthy that in some cases the ELR− ligands have pro-tumorigenic properties, such as ELR-CXCL12/CXCR4 [20], ELR-CXCL11/12-CXCR7 [44], and ELR-CXCL13/CXCR5 [49], increasing angiogenic and metastatic activities in the tumor [50,51].