What is a solitary fibrous tumor?

From the Guidelines

A solitary fibrous tumor (SFT) is a rare type of soft tissue tumor that exhibits a low risk for local recurrence, with the aim of resection being complete resection with negative margins while preserving uninvolved organs. These tumors originate from mesenchymal cells, which are cells that develop into connective tissues like blood vessels, muscles, and fat [ 1 ]. SFTs most commonly occur in the pleura (the membrane surrounding the lungs), but they can also develop in other locations including the meninges (brain and spinal cord coverings), peritoneum, orbit, and virtually any soft tissue site.

Key Characteristics of SFTs

• Most SFTs are benign (non-cancerous), growing slowly and causing symptoms primarily through pressure on surrounding structures [ 1 ].
• Approximately 10-20% of these tumors can be malignant, with the potential to recur after treatment or metastasize to other parts of the body.
• Diagnosis typically involves imaging studies followed by a biopsy to confirm the tumor type.
• Treatment usually consists of complete surgical removal, with additional therapies like radiation or chemotherapy sometimes recommended for malignant variants [ 1 ].

Treatment and Management

• The activity of radiotherapy in SFT should be considered in the preoperative planning [ 1 ].
• Targeted therapies, such as anti-angiogenic TKI, may also be considered for the treatment of SFT [ 1 ].
• Long-term follow-up is important as recurrence can occur years after initial treatment, particularly for tumors with concerning pathological features such as high cellularity, increased mitotic activity, or necrosis. Some key points to consider when managing SFTs include:
• Complete surgical removal with negative margins is the primary goal of treatment [ 1 ].
• Preservation of uninvolved organs is important to minimize morbidity and improve quality of life [ 1 ].
• The use of targeted therapies, such as anti-angiogenic TKI, may be considered for the treatment of SFT [ 1 ].

From the Research

Definition and Characteristics of Solitary Fibrous Tumors

• Solitary fibrous tumors (SFTs) are rare mesenchymal neoplasms that can arise from any part of the body, but most commonly occur in the pleura 2, 3, 4.
• SFTs are classified into two forms: pleural and extrapleural, and they morphologically resemble each other 3.
• These tumors are generally considered to be benign, but they can be borderline-malignant and may cause serious complications if not treated 3, 5.
• SFTs are characterized by the coexistence of sparse and dense areas, and they can be identified by immunohistochemical markers such as CD34, CD99, Bcl-2, and vimentin 4.

Diagnosis and Treatment of Solitary Fibrous Tumors

• The diagnosis of SFTs is usually accidental, as they often do not produce clinical symptoms 3, 4.
• Complete surgical resection is the mainstay of treatment for SFTs, and it is usually sufficient to achieve a cure 2, 3, 4, 6.
• The surgical approach can vary depending on the size and location of the tumor, and it may involve thoracotomy, sternotomy, video-assisted thoracoscopic surgery, or a robotic approach 2.
• Radiotherapy and chemotherapy may be considered as adjuvant treatments, but their effectiveness is unclear due to the rarity of the tumor and lack of data 3, 5.

Prognosis and Recurrence of Solitary Fibrous Tumors

• The prognosis of SFTs is generally good, with a low recurrence rate if the tumor is completely resected and the degree of differentiation is favorable 2.
• However, recurrence can occur, especially if the tumor is not completely resected, and redo surgery may be necessary to achieve a favorable prognosis 2.
• The risk of recurrence and metastasis is higher in malignant SFTs, which can be identified by characteristics such as adhesion or unclear boundary with surrounding tissues, pleural effusion or calcification, and high Ki67 proliferation index 4.