Synovial sarcoma of the pleura and its differentiation from other primary pleural tumours: a clinicopathological and immunohistochemical review of three cases.

AIMS: Synovial sarcomas are rare tumours occasionally arising in the pleural cavity, a site where their histological characteristics may be mistaken for those of malignant mesothelioma. We examined three cases of primary pleural synovial sarcoma in order to look for clinicopathological features that may help in distinguishing them from both mesotheliomas and other sarcomas that may arise in the pleura. METHODS AND
RESULTS: All three patients were male, aged 42, 28 and 42, respectively, and had no known exposure to asbestos. One biphasic tumour contained neutral mucin in focal epithelial elements that also stained positively for BerEP4 and AUA1. All three tumours showed focal positivity for either keratin or EMA in the sarcomatous elements, and they also stained positively for bcl-2 protein and MIC2 gene product (CD99).
CONCLUSIONS: Our results emphasize the importance of being aware of synovial sarcoma as a possible primary pleural malignancy, especially in a young patient with a localized mass. In addition, the presence of bcl-2 protein perhaps represents a useful marker in distinguishing synovial sarcoma, especially monophasic variants, from mesothelioma within a panel of antibodies.