CHEMICALLY-INDUCED PULMONARY MUCOEPIDERMOID CARCINOMA IN A FEMALE WISTAR RAT

A case of a mucoepidermoid carcinoma, conventionally classified as an adenosquamous carcinoma, is described. The tumour bearing rat was expo sed to a mixture of a pyrolized pitch condensate rich in polycyclic ar omatic hydrocarbons and carbon black particles by inhalation for 10 mo nths. The neoplasm was examined by conventional histopathologic proced ures and by immunohistochemical detection of intermediate filaments. M orphologically, the tumour consisted of two components. The centre of the neoplasm was predominantly of adenocarcinomatous tissue and this w as surrounded by keratinized squamous epithelium. The predominantly ad enocarcinomatous component had a characteristic structural pattern con sisting of one or a few layers of squamous epithelium covered by a con tinuous layer of mature goblet cells. The flattened cells were recogni zable as squamous cells on the light microscopic level only after immu nohistochemical staining with cytokeratin antibodies. Goblet cells and extracellular mucin were intensely positive for the PAS-reagent. This mucoepidermoid carcinoma in the rat was morphologically similar to th ose described in man. It is still unclear whether pulmonary mucoepider moid carcinomas of humans originate from the bronchial epithelium or b ronchial glands. It is most probable that the mucoepidermoid carcinoma of a rat described in this communication occurred by metaplasia in a carcinoma of bronchiolo-alveolar origin.