Biochemical and ultrastructural differences between muco-epidermoid and carcinoid tumors of the bronchus.

Bronchial adenomas have been classified into three types: carcinoid tumors, cylindromas (adenoid cystic carcinomas), and mucoepidermoid tumors. Studies from our laboratory have demonstrated that the quantitative measurement of monoamine oxidase (MAO) in homogenates of carcinoid tumors of foregut origin is different than the activity enzymes in other tumors of neural crest origin. In this study we compared the biochemical composition of 12 bronchial carcinoid tumors with the biochemical composition of a rare mucoepidermoid adenoma of the bronchus. Electron microscopy revealed that some cells of the mucoepidermoid adenoma contained mucin and tonofilaments; none of the cells contained neurosecretory granules. The MAO activity of the bronchial carcinoid tumors was much higher than the MAO activity of the mucoepidermoid adenoma. Thus, there are distinctive ultrastructural and biochemical differences in these two types of bronchial adenomas.