Pulmonary blastoma with argyrophil cells and lacking sarcomatous features (pulmonary endodermal tumor resembling fetal lung).

A tumor of the lung in a 35-year-old woman contained numerous complex, branching tubules resembling the developing fetal lung in its canalicular state. Some of the epithelial cells within the tubules were argyrophilic, and electron microscopy demonstrated the dense-core neurosecretory-type cytoplasmic granules. These characteristics support an endodermal origin for this neoplasm. Morphologically the tubules are similar to the epithelial component seen in pulmonary blastoma, but the tumor lacks the sarcomatous areas integral to the concept of blastoma. The designation pulmonary endodermal tumor resembling fetal lung may better describe this unusual neoplasm.