ANPEP and squamous cell carcinoma: Since human squamous cell carcinoma cells, including NCl-H292 pulmonary cancer cells, do not exhibit APN/CD13 [93], increased uptake of the NCI-H292 tumors could be attributed to the profuse tumor angiogenesis and associated APN/CD13 positivity of vascular endothelial cells, such as human umbilical vein endothelial cells (HUVEC) and human aortic endothelial cells (HAEC) [94].