Atypical mesothelial hyperplasia associated with bronchogenic carcinoma.

Atypical mesothelial hyperplasia encountered in pleural fluid or in a pleural biopsy specimen raises the suspicion that one may be dealing with a diffuse malignant mesothelioma of the pleura. We studied eight cases with cytologic or histologic changes of mesothelial atypia thought to be suspicious for diffuse malignant mesothelioma. In each case, the hyperplasia was associated with a bronchogenic carcinoma in the lung subjacent to the mesothelial hyperplasia. Bronchogenic carcinoma should be added to the list of causes of atypical mesothelial hyperplasia. This combination of reactive and malignant processes should be appreciated, since pleural carcinomatosis and diffuse malignant mesothelioma must be separated for clinical and epidemiologic reasons.