ANPEP and neoplasm: A positive immunostaining (i. e. 2+/3+, according to the criteria described above) of tumor tissues with the monoclonal CD13 antibody was found for endothelial cells and vessel-associated stroma cells in n = 41 cases (15%) and in NSCLC tumor cells in n = 20 cases (7%), the latter with a predominantly membranous immunostaining (Fig 1A–1F).