SOLITARY FIBROUS TUMOR (LOCALIZED FIBROUS TUMOR) OF THE PLEURA
Solitary fibrous tumor of the pleura is a rare neoplasm that arises most commonly within the visceral pleura but may evolve from the parietal pleura of the chest, mediastinum or diaphragm. These tumors are most commonly diagnosed in the sixth to seventh decade with equal rates of occurrence for both sexes. Unlike malignant mesothelioma, the solitary fibrous tumor of the pleura has not been linked with environmental exposures. This tumor is frequently identified on routine chest x-ray or is associated with vague symptoms consisting of chest pain, dyspnea or cough in approximately 50-75% of patients. Although they may give the appearance of gross infiltration on radiologic studies, most are well encapsulated or pedunculated allowing for routine surgical removal. Grossly, the tumors tend to be firm, smooth, rounded masses which measure five to ten centimeters in diameter(Image 11). Histologically, the tumor appears as a mixture of spindle cells interspersed within a variable amount of collagen. The growth pattern is predominantly haphazard (patternless ) or hemangiopericytic but focal areas of storiform growth may be present. These cells are typically both vimentin and CD34 positive and cytokeratin negative by immunohistochemical staining. Cellular atypia and cystic degeneration or necrosis are not common findings and may suggest malignancy. Criteria for malignancy include high cellularity, high mitotic activity (>4 mitoses per 10 high power fields), pleomorphism, hemorrhage, and necrosis. In one study, 82 of 223 solitary fibrous tumors were considered malignant applying these criteria. Of 169 patients available for follow-up, 100% of benign and 45% of malignant tumors were cured by a single excision, with 55% of patients with malignant tumors succumbing to disease due to invasion or metastasis.
An example of a malignant solitary fibrous tumor is pictured below. Pictured is a grossly well circumscribed mass that is highly cellular with a haphazard growth pattern.(Image 12) Note the multiple mitoses present in this high power field.(Image 13) Although margins of resection were microscopically free of tumor this tumor recurred a short time after the first excision and was associated with a malignant pleural effusion Pictured is a smear of the cells within the pleural effusion (Image 14) and an H & E stain of the cell block from the same pleural effusion.(Image 15)
Contributed by David Krisky, MD, PhD and Sheldon Bastacky, MD