Malignant mesothelioma with osteoblastic heterologous elements

A 59 year-old man with a history of asbestos exposure presented with a righ t pleural effusion and a diffuse pleural thickening with focal calcificatio ns on chest X-ray. Cytological examination of pleural fluid indicated malig nant mesothelioma. A biopsy specimen showed malignant mesothelioma surround ing a fragment of mature bone. The patient was treated with intrapleural in terferon, but relapsed 3 Wars later. A fresh biopsy specimen showed round t umor cells surrounding osteoid substance. Only ten cases of this rare varia nt of malignant mesothelioma with osteoblastic heterologous elements have b een reported in the literature. The most difficult differential diagnosis i s primary pleural osteosarcoma.