Spindle cell tumors of the pleura: differential diagnosis

Spindle cell tumors that arise in or metastasize to the pleura must be thoroughly evaluated to arrive at a definitive diagnosis. Malignant mesothelioma is the most common tumor arising in the pleura, but metastatic tumors to the pleura occur more frequently. Additionally, many tumors arising in the lung and surrounding tissues involve the pleura. It is crucial to arrive at a correct diagnosis since many of these neoplasms show different prognoses and require varying treatment modalities. Sarcomatoid malignant mesothelioma is a rare tumor that arises in the pleura, and can be confused with numerous tumors arising in or metastasizing to the pleura, including synovial sarcoma, metastatic sarcomatoid carcinoma, metastatic melanoma, thymoma, renal cell carcinoma, localized fibrous tumor, leiomyosarcoma, and other types of sarcoma. Desmoplastic malignant mesothelioma is a fibrous sarcomatoid variant of malignant mesothelioma, and is occasionally mistaken for chronic fibrous pleurisy. Here, we review morphological, clinical, histological, immunohistochemical, ultrastructural, and molecular methods that aid in the diagnosis of spindle cell tumors of the pleura, and we provide specific examples of patients in which this multi-modal approach proved to be helpful.