Malignant fat-forming solitary fibrous tumor of the thigh.

Fat-forming solitary fibrous tumor (SFT), previously known as lipomatous hemangiopericytoma, was described as an uncommon variant of extrapleural SFT in the 2013 World Health Organization (WHO) classification of soft tissue tumors.1 Fat-forming SFT is an uncommon, slow-growing neoplasm and is characterized by the typical histologic features of SFT with a mature adipocytic component. The fat-forming variant of SFT exhibits benign biological behavior; however, in rare case, it can have malignant histologic features. Fewer than 20 malignant cases have been reported in the English literature.2-5 Herein, we present a case of fat-forming SFT with malignant histologic features arising in the thigh, in addition to a review of the literature.