FLT1 and neoplasm: We also observed that MDSC-secreted VEGFA and multiple chemokines CCL2, CXCL1, CXCL2, CXCL3, and CXCL8 could act on endothelial cells via VEGFA-KDR/FLT1 and CCL2/CXCLs-ACKR1 interactions, which were crucial for tumor angiogenesis [42, 43].