Sarcomatoid Mesothelioma With Osteosarcomatous Differentiation

We present a case of sarcomatoid mesothelioma (SM) of the pleura arising in 74 year-old man. The patient presented with pleural effusion and a 8 cm mass adherent to the parietal pleura was discovered by CT scan. After a first trans-thoracic biopsy in which only necrotic tissue and fungal hyphae were found, the patient underwent to video-assisted thoracotomy and small fragments of tissue were taken for histological diagnosis. Finally, a diagnosis of sarcomatoid neoplasms of mesothelial origin was rendered. At surgery, the mass was removed together with a second nodule of 4 cm in major axis, adherent to the visceral pleura , close to the wall of the esophagus. Histologically, the parietal mass appeared composed of epithelioid to spindled cells having abundant cytoplasm and vesicular nuclei with prominent nucleoli. The 4 cm , para-esophageal nodule was composed of spindled cells arranged in short fascicles, intermingled with osteoid material. In both tumours, mitoses were frequent and areas of necrosis were also present. The pleural tissue adjacent to the nodules was diffusely thickened, but no evidence of malignant proliferations was evident in it. The immunophenotype of the two nodules was identical: Neoplastic cells were positive with cytokeratin 7 and vimentin, while calretinin, Bcl2, CD99 and TTF1 were negative. Osteosarcomatous differentiation in mesothelioma is not frequent. SMs have to be distinguished from true pleural sarcomas and mainly from synovial sarcoma.