Mucoepidermoid carcinoma of the bronchus: an electron microscopic study of the low grade and the high grade variants.

Two cases of mucoepidermoid carcinoma of the bronchus--one a low grade tumor and the other a high grade tumor--are presented with findings by light and electron microscopy. This represents the first report of the ultrastructure of mucoepidermoid carcinoma of the bronchus and demonstrates the ultrastructural similarities between the low grade exophytic tumor confined to the bronchus and the high grade infiltrating tumor with lymph node and pulmonary metastases. The ultrastructural features are similar to those described for mucoepidermoid carcinoma of the salivary gland and are consistent with the proposed origin of the tumor from the submucosal bronchial gland duct. These two cases and a review of previously reported cases indicate that, analogous to mucoepidermoid carcinoma of the salivary glands, mucoepidermoid carcinoma of the bronchus may occur as either a low grade or high grade variant which can be identified on the basis of growth characteristics and histologic features.