[Malignant mesothelioma with osteoblastic heterologous elements]

A 59 year-old man with a history of asbestos exposure presented with a right pleural effusion and a diffuse pleural thickening with focal calcifications on chest X-ray. Cytological examination of pleural fluid indicated malignant mesothelioma. A biopsy specimen showed malignant mesothelioma surrounding a fragment of mature bone. The patient was treated with intrapleural interferon, but relapsed 3 years later. A fresh biopsy specimen showed round tumor cells surrounding osteoid substance. Only ten cases of this rare variant of malignant mesothelioma with osteoblastic heterologous elements have been reported in the literature. The most difficult differential diagnosis is primary pleural osteosarcoma.