AXL and neoplasm: In light of these studies, we analyzed an array of immuno-modulatory proteins, which have been associated with tumor phenotypes and could be exploited for tumor therapy, including IGFBP-1, programmed cell death ligand 1 (PD-L1), the soluble tyrosine receptor kinase AXL, interferon-α (IFN-α), granulocyte-macrophage colony-stimulating factor (GM-CSF), and prostaglandin E2 (PGE2).