Adenomyoepithelioma of the lung

A 66-year-old man with an extremely rare neoplasm of the lung, adenomyoepithelioma, is described. The tumor was a well-circumscribed lesion that showed solid, glandular, and papillary growth patterns and was composed of two types of cells, inner epithelial cells and outer myoepithelial cells. This bidirectional differentiation was confirmed immunohistochemically. The inner epithelial cells were positive for carcinoembryonic antigen and epithelial membrane antigen, while the outer myoepithelial cells were S-100 protein-positive. Electron microscopically, the tumor was characterized by a large amount of microfilaments in the cytoplasm and layers of basement membrane-like material in the intercellular spaces. Some glycogen granules were detected.