A papillary endobronchial tumor with a transitional cell pattern

An endobronchial papillary tumor in a 75-year-old reformed cigarette smoker exhibited the light microscopic features of a transitional cell neoplasm. The constituent cells showed cytologic features of malignancy; in addition, there were microfoci of mucosal invasion. Electron microscopy showed tonofilaments and numerous desmosomes. There were no ultrastructural features similar to those seen in tumors of urothelial origin, and the similarity with the latter was only at the light microscopic level, the tumor being a variant of a squamous carcinoma. Previous descriptions of so-called transitional cell neoplasms of the lower bronchial tree included a cytologically benign lesion an one showing carcinoma in situ. The present case indicated that the spectrum of these neoplasms includes lesions that show microinvasion. Therefore, exophytic papillary endobronchial tumors should be distinguished as a group of distinct variants of squamous carcinoma.