Secretory component in pulmonary adenocarcinoma and mesothelioma

The distribution of secretory component was examined by an immunoperoxidase method in 40 pulmonary adenocarcinomas, 11 malignant pleural mesotheliomas and areas of normal lung adjacent to the tumours. Secretory component was demonstrated in tumour cells in 25 (67%) adenocarcinomas. Its presence correlated with the degree of differentiation but was not related to tumour pattern. In the normal lung secretory component can be demonstrated in bronchial ciliated cells, bronchial gland serous cells, bronchiolar epithelium and hyperplastic alveolar epithelium. Although not usually detectable in normal mucous cells it was frequently present in mucin‐producing tumours. None of the mesotheliomas examined contained secretory component and this may be an additional useful feature in the differential diagnosis between mesothelioma and adenocarcinoma.