CD13 (Cluster of Differentiation 13) is a broad specificity aminopeptidase that plays a role in final digestion of peptides generated from hydrolysis of proteins by gastric and pancreatic proteases. This antibody detects a 150 kDa protein, it is used as a marker for acute myeloid leukemia. CD13 is expressed in epithelial cells of the kidney, intestine, and respiratory tract; granulocytes, monocytes, fibroblasts, endothelial cells, cerebral pericytes at the blood-brain barrier, synaptic membranes of cells in the CNS, endometrial stromal cells, vasculature of tissues that undergo angiogenesis, in malignant gliomas and lymph node metastases from multiple tumor types, and in plasma. It is found to be elevated in plasma and effusions of cancer patients.