SFTs

Solitary fibrous tumors (SFTs) are rare mesenchymal neoplasms that most commonly arise from the pleura but can occur virtually anywhere, including the soft tissues, meninges, liver, and extremities. They are usually slow-growing and may be asymptomatic or present with symptoms related to mass effect or location. A subset may produce insulin-like growth factor 2 and cause non-islet cell tumor hypoglycemia.

Histologically, SFTs show spindle- or ovoid-shaped cells in a variably cellular collagenous stroma with a patternless arrangement and prominent branched, 'staghorn' blood vessels. Immunohistochemistry typically demonstrates CD34 positivity; a highly specific diagnostic feature is strong nuclear staining for STAT6, reflecting a NAB2-STAT6 gene fusion.

Diagnosis relies on imaging to define extent and biopsy with histology and immunohistochemistry to confirm SFT and exclude other spindle-cell neoplasms. Routine staging may be used to assess metastasis when malignant behavior is suspected.

Surgical excision with negative margins is the mainstay of treatment. Most SFTs behave indolently, but a subset exhibits malignant features, such as high mitotic activity, cellular atypia, necrosis, or large size, and carries higher risks of recurrence and metastasis. In unresectable or metastatic disease, treatment choices are individualized and evidence is limited; options that have shown activity include anti-angiogenic agents and various chemotherapy regimens.

Prognosis ranges from excellent after complete resection to guarded for malignant SFTs. Long-term follow-up is recommended due to the possibility of late recurrence.

The term 'solitary fibrous tumor' was adopted by WHO; earlier reports used hemangiopericytoma for some lesions. A defining molecular feature is the NAB2-STAT6 fusion, with STAT6 immunostaining used as a diagnostic tool.