Benign clear cell tumor of the lung. A histopathologic study.

Benign clear cell tumor of the lung is extremely rare, and its histogenesis is still in dispute. We experienced a case of this neoplasm in the lung of a 28-year-old man, and carried out a study using both light and electron microscopy and immunohistochemistry. Histologically, the tumor was composed of sheets of large round or polygonal cells with abundant clear cytoplasm surrounded by thin-walled blood vessels. Electron microscopy showed granules (180 nm in diameter) in the cytoplasm. Immunohistochemically, S-100 protein-positive tumor cells were seen, but other neural markers and the markers for epithelial, muscular, vascular, histiocytic and endocrine cell origins were negative. The histogenesis of this pulmonary neoplasm could not be definitively determined, but its neural cell origin remains a possibility.