BCL-2 EXPRESSION IN PLEURAL AND EXTRAPLEURAL SOLITARY FIBROUS TUMORS

This study evaluated the immunoreactivity for bcl-2, a molecule involv ed in the control of programmed cell death, in cases of pleural (14) a nd extrapleural (2) solitary fibrous tumour (SFT), malignant mesotheli omas of different histological types, and a variety of extrapleural CD 34-positive and CD34-negative spindle-cell tumours. In all SFTs, stron g and diffuse immunostaining was demonstrated with anti-bcl-2 antibody , sharply contrasting with the complete lack of staining observed in a ll mesotheliomas. The specificity of immunodetection of bcl-2 in SFT w as confirmed by immunoblot analysis, showing a band consistent with th e bcl-2 protein. At extrapleural locations, strong bcl-2 immunoreactiv ity was observed in Schwannoma (2/3 cases), synovial sarcoma (4/4 case s), and all cases of CD34-positive gastrointestinal stromal tumour (GI ST; 10/10 cases). Most sarcomas were bcl-2-negative. Lack of bcl-2 exp ression was demonstrated in tumours which can pose problems in the dif ferential diagnosis of SFT and can exhibit haemangiopericytoma-like fe atures, including haemangiopericytoma (3 cases), dermatofibrosarcoma p rotuberans (16 cases), and deep-seated fibrous histiocytoma (3 cases). The constitutive expression of bcl-2 in SFT widens the spectrum of av ailable markers for these tumours, providing a useful adjunct to their differential diagnosis in difficult cases at pleural and extrapleural sites, and contributing to the understanding of their histogenesis an d molecular pathogenesis. (C) 1997 by John Wiley & Sons, Ltd.