AB 57. Difficulties in biphasic mesothelioma diagnosis

Objective: Presentation of a case of biphasic pleural mesothelioma with reference to difficulties concerning differential diagnosis from reactive mesothelial proliferations.

Patients and methods: We present a case of a 76-year-old woman, which was found with total thickening of her left pleura and nodular infiltrations with hemorrhagic fluid in her CT-scan of thorax. Histological examination of bioptic material revealed high cellular tissue presence with parietal pleura texture. There were also several cells with epithelioid appearance, large clear nuclei with small nucleoli inside a fibrous layer. Immunohistochemical stains were positive for Vimentin, Ck7, Ck5/6, Calretinin, and WT-1. EMA had moderate membrane staining, whereas proliferation index Ki-67 was highly expressed.

Results: The above morphological and immunohistochemical results do not clarify the differential diagnosis between biphasic pleural mesothelioma from reactive mesothelial proliferations.

Conclusions: Reactive mesothelial proliferations may mimic malignant mesothelioma. High cellularity, the presence of numerous mitotic figures, cytologic atypia and the presence of necrosis are features of both reactive mesothelial proliferations and malignant mesothelioma. On the other hand, demonstration of stromal infiltration and positive staining in markers such as EMA and p53 strongly indicate the presence of malignant mesothelioma. In any case, it is mandatory to take in advance clinical, imaging and operative features, in order to establish safely a diagnosis.