Solitary fibrous tumors (SFTs), initially observed in the pleura, were later found to develop in almost any extrapleural site. Dedifferentiation within SFTs, a rare phenomenon, was characterized only recently, although it was previously described in soft tissue and bone tumors. We report a case of dedifferentiated SFT arising in the right pleura of a 69-year-old man. Computed tomography revealed a huge mass in the thoracic cavity. The tumor contained an area with a high degree of calcification and was heterogeneously enhanced. Macroscopically, the resected tumor was 175×145×135 mm in size. Morphologically and immunohistochemically, this was comprised of a typical SFT juxtaposed to a high-grade component including an osteosarcomatous component. These were sharply demarcated by thin fibrous septa. Furthermore, NAB2-STAT6 fusion transcripts were detected by reverse-transcriptase polymerase chain reaction in both conventional and high-grade components, supporting the concept of a dedifferentiation process in this tumor.
Keywords: NAB2-STAT6; Solitary fibrous tumor; dedifferentiation.