Malignant Solitary Fibrous Tumor of the Pleura in Mediastinum

ABSTRACT

Solitary fibrous tumors (SFTs) most often involve the pleura and also may encompass the peritoneum and nonserosal sites. They occur as solitary encapsulated tumors and pursue a relatively benign clinical course. The usual criteria for malignancy are high cellularity, mitotic activity (more than 4 per 10 high-power fields), cellular pleomorphism, hemorrhage and necrosis as well as infiltrative growth. We report a case of malignant SFT of pleura who presented with an anterior mediastinal mass. Grossly, it was a 10x8x6.5 cm sized, encapsulated and well-demarcated, solid neoplasm with areas of extensive necrosis. Microscopically, parallel or haphazard arrangement of spindle cells with variable degrees of collagenous background were noted. Storiform fascicle formation, hemangiopericytoma-like pattern, and epithelioid cell clusters were often intermingled. Nodular areas with high cellularity and mitotic activity (> or =10/10 HPFs) were scattered throughout the neoplasm, however no definite cellular pleomorphism was encountered. Tumor cells were immunoreactive for vimentin and CD-34, which distinguished them from the mesothelial cells. Electron microscopically, they revealed fibroblastic and myofibroblastic differentiation.