Solitary fibrous tumor (SFT) varies from clinically benign to uncertain biologic potential and overt sarcoma, although the latter is a rare occurrence. Giant cell angiofibroma is a morphologic variant of SFT. The World Health Organization (WHO) classification essentially merges SFT and hemangiopericytoma (HPC). Central nervous system HPCs, however, should be classified separately based on their unique clinicopathologic profile, including higher biologic potential with metastatic capability. Sinonasal HPC is a myopericytic or smooth muscle tumor and is discussed in Chapter 23.

SOLITARY FIBROUS TUMOR

SFT is a CD34-positive fibroblastic neoplasm that can present in a wide variety of soft tissue and visceral locations, with a spectrum that ranges from benign to malignant.

History and Terminology

Originally known as a neoplasm of the pleura and mediastinum, SFT was historically designated as (benign or malignant) fibrous mesothelioma. Its nonepithelial and nonmesothelial nature and lack of association with asbestosis prompted its renaming as localized fibrous tumor, and more recently as SFT. Similar tumors were subsequently reported on peritoneal serous surfaces, peripheral soft tissues, and in a wide variety of visceral sites in different organ systems.

Although most SFTs are benign, some recur locally and a few behave as soft tissue sarcomas and metastasize, indicating that this tumor has a clinical spectrum from benign to fully malignant. A mitotic rate of >4 per 10 HPFs, tumor necrosis, and atypia have been identified as risk factors for malignant behavior in pleural examples, and similar criteria have been used in other sites.