FLT1 and neoplasm: Since its discovery from human pheochromocytoma extracts, cumulative clinical evidence has revealed the association between AM and a variety of tumor types, showing that it is expressed by malignant cells, endothelial cells, pro-angiogenic cancer-associated fibroblasts (CAFs) and tumor-associated macrophages (TAMs), immature monocytic cells including TIE2+ monocytes, VEGFR1+ hemangiocytes, and CD11b+ myeloid cells within the tumor microenvironment (119–122).