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What is solitary fibrous tumor?
A solitary fibrous tumor (SFT) is an uncommon tumor that grows from the body's connective (fibrous) tissue. It can arise almost anywhere, but the classic locations are around the lining of the lung (the pleura), in the lining of the brain and spinal cord (the meninges), and in soft tissues of the limbs, abdomen, and pelvis. SFT was historically described under several names, including 'hemangiopericytoma,' and these are now understood to be the same family of tumor, unified by a characteristic gene fusion called NAB2-STAT6 that can be confirmed on a biopsy. Most solitary fibrous tumors grow slowly and behave in a benign or low-grade way: they form a well-defined mass that can be cured by complete surgical removal. However, a minority behave more aggressively — they can grow back at the original site or, less commonly, spread to distant organs such as the lungs, liver, or bone, sometimes many years after the first treatment. Because of this long, sometimes unpredictable course, SFT requires long-term follow-up even after a seemingly complete removal. Pathologists use features such as the tumor's size, how many cells are dividing, and whether there are areas of dead tissue to estimate the risk of recurrence or spread. The cornerstone of treatment is surgery to remove the tumor completely; radiation is used when a tumor cannot be fully removed, when it sits in a delicate location such as the brain or spine, or to lower the chance of an aggressive tumor returning, and newer targeted antiangiogenic drugs are options for disease that has spread.
The main types
Doctors group solitary fibrous tumor by where it starts and how it behaves:
| Type | What it means, simply |
|---|---|
| Pleural solitary fibrous tumor | Arises around the lining of the lung and can grow quite large before causing breathlessness or chest discomfort; most are cured by surgery, and a rare subset can cause low blood sugar by releasing an insulin-like substance. |
| Meningeal (brain or spine) solitary fibrous tumor | Grows from the coverings of the brain or spinal cord and can resemble a meningioma; these have a higher tendency to recur and to spread later, so surgery is often followed by radiation and close surveillance. |
| Soft-tissue solitary fibrous tumor | Found in the limbs, abdomen, pelvis, or other soft tissues; behavior ranges from gentle to aggressive depending on the tumor's features, which guide whether radiation is added. |
| Malignant / dedifferentiated solitary fibrous tumor | An aggressive form with rapidly dividing cells and a higher risk of returning and spreading; treated more intensively with surgery, radiation, and systemic therapy for advanced disease. |
Staging, in plain terms
Solitary fibrous tumor is not staged with one simple number the way many cancers are. Instead, doctors estimate the risk that a given tumor will come back or spread, using a combination of features rather than a single stage. The most important of these are how quickly the tumor's cells are dividing (the mitotic rate), the size of the tumor, the patient's age, and whether the pathologist sees areas of dead tissue (necrosis) within it. Tumors with a low mitotic rate, smaller size, and no necrosis are very likely to behave gently and be cured by surgery, while those with a high mitotic rate, large size, or necrosis carry a higher risk of recurrence or distant spread. Location also matters: tumors in the coverings of the brain and spine tend to recur and to spread more often than typical soft-tissue ones, and SFTs arising in the limbs and trunk are additionally assessed with the soft-tissue sarcoma TNM system, which considers size and depth (T), lymph nodes (N), and distant spread (M). Two further points shape care. First, SFT can recur or spread very late — sometimes a decade or more after treatment — so follow-up is long. Second, when it does spread it favors the lungs, liver, and bone, so imaging of those areas guides decisions. The practical questions are: where is the tumor, can it be removed completely, what do its features predict about future behavior, and has it spread.
| No single universal stage number — risk is estimated from the tumor's location, size, how fast its cells divide (mitotic rate), patient age, and whether dead tissue is present; soft-tissue sarcoma TNM is applied to limb and trunk tumors | What it generally means |
|---|---|
| Low-risk, localized | A small, slow-dividing tumor with no dead tissue, confined to its site; usually cured by complete surgery alone, with long-term follow-up. |
| Intermediate- or high-risk, localized | A larger or faster-dividing tumor still confined to its site; treated with complete surgery, often followed by radiation to lower the chance of it returning. |
| Incompletely removable or delicate location | A tumor that can't be fully removed, or sits in a sensitive spot such as the brain or spine; radiation is used to control disease left behind or to treat it without further surgery. |
| Metastatic | Cancer that has spread — most often to the lungs, liver, or bone, sometimes years later; treated with targeted antiangiogenic drugs, with surgery or focused radiation for a limited number of deposits. |
The standard of care
Solitary Fibrous Tumor is almost always treated by a team that may include a surgeon, a medical oncologist, and a radiation oncologist, combining therapies for the best result. The usual building blocks are:
Complete surgical removal
Taking out the tumor completely with a margin of healthy tissue is the main treatment and cures most solitary fibrous tumors; for tumors in the brain or spine, the completeness of removal strongly affects the chance of recurrence.
Radiation therapy
Used after surgery to lower the chance of an aggressive or incompletely removed tumor returning, and as the main treatment when a tumor can't be safely removed or sits in a delicate location.
Expert pathology with molecular testing
Confirming the diagnosis — including the characteristic STAT6 marker and NAB2-STAT6 gene fusion — and assessing the tumor's risk features is essential, because it determines how intensively to treat and how closely to follow up.
Targeted antiangiogenic therapy
Because these tumors are rich in blood vessels, drugs that block blood-vessel growth can shrink or stabilize disease that has spread, and are a mainstay of treatment for metastatic SFT.
Long-term surveillance
Because SFT can return or spread many years after treatment, regular imaging over a long period is important so that a recurrence or new deposit is caught while it is small and treatable.
How radiation treatment works
Radiation therapy treats solitary fibrous tumor by delivering precisely aimed beams of energy that damage the DNA inside tumor cells so they can no longer grow and divide. Because most solitary fibrous tumors are cured by surgery alone, radiation is used selectively — but in the right situations it is an important tool. The first is to lower the chance of recurrence after surgery for tumors that carry higher risk, such as those that divide quickly, are large, contain areas of dead tissue, or could not be removed with a clear margin. Like other connective-tissue tumors, an aggressive SFT can leave microscopic disease behind at the edges of the surgical field; radiation treats that wider zone so the tumor is less likely to grow back at the original site. The second situation is when a tumor cannot be safely removed — for example, when it is wrapped around critical structures — or when it sits in a delicate location such as the coverings of the brain or spine. There, focused radiation can control the tumor for long periods and relieve symptoms caused by pressure on nearby tissue. For tumors in the brain and spine, stereotactic radiosurgery delivers a concentrated dose in one or a few sessions while sparing the surrounding nervous tissue, which is especially valuable because meningeal solitary fibrous tumors have a particular tendency to recur. Radiation also has a role beyond the original site: because SFT tends to grow slowly even when it spreads, a limited number of deposits in the lungs, liver, or bone can often be controlled with focused, high-dose stereotactic body radiation rather than surgery. Throughout, modern planning shapes the dose tightly around the target so that nearby healthy tissue is spared, which matters given how often these tumors sit close to the lung, brain, or spinal cord.
The main ways radiation is delivered for solitary fibrous tumor:
Postoperative (adjuvant) radiation
Radiation to the tumor bed after surgery sterilizes microscopic disease left behind, lowering the chance of recurrence for aggressive tumors or when margins are close.
Definitive radiation
When a tumor can't be safely removed, focused radiation can control it for long periods, shrinking it and relieving symptoms it causes by pressing on nearby structures.
Stereotactic radiosurgery (SRS) for brain or spine tumors
Highly focused, high-dose radiation delivered in one or a few sessions controls meningeal solitary fibrous tumors and their recurrences precisely while sparing surrounding brain or spinal cord.
Stereotactic body radiation (SBRT) for metastases
Focused, high-dose beams can ablate a limited number of deposits in the lungs, liver, or bone without surgery, providing durable control of the slow-growing spots SFT tends to form.
Latest studies shaping care
Care keeps improving — often toward getting the same excellent results with less burden on patients. A few developments:
NAB2-STAT6 fusion unifies the diagnosis: The discovery that solitary fibrous tumor and what used to be called hemangiopericytoma share the NAB2-STAT6 gene fusion allows a confident diagnosis from a biopsy using the STAT6 marker, clarifying treatment for tumors that were once classified separately.[1]
Molecular pathology studies defining the SFT/hemangiopericytoma spectrum
Radiation lowers recurrence after surgery: For higher-risk and incompletely removed solitary fibrous tumors, adding radiation after surgery improves local control, supporting its selective use even though many SFTs are cured by surgery alone.[2]
Postoperative radiotherapy outcome series in SFT
Antiangiogenic drugs for advanced disease: Because these tumors depend on a rich blood supply, drugs that block blood-vessel growth can shrink or stabilize metastatic solitary fibrous tumor, and have become a standard option for disease that has spread.[3]
Antiangiogenic therapy trials in advanced SFT
Common questions
Is a solitary fibrous tumor cancer? It sits on a spectrum. Most solitary fibrous tumors behave in a benign or low-grade way and are cured by completely removing them. But a minority are more aggressive and can return at the original site or, less often, spread to distant organs — which is why the whole family is taken seriously and followed long-term. Pathologists estimate the risk for each tumor using features such as its size, how quickly its cells are dividing, and whether there are areas of dead tissue. Knowing that risk tells the team whether surgery alone is enough or whether radiation and closer follow-up are warranted.
I was told my tumor used to be called a hemangiopericytoma — is that the same thing? Yes. 'Hemangiopericytoma' was an older name for tumors that are now understood to be part of the solitary fibrous tumor family. Modern testing showed they share the same characteristic gene fusion, NAB2-STAT6, so they have been grouped together. The change in name doesn't change your tumor — it reflects a better understanding of it — and it helps your team apply what is now known about how these tumors behave and respond to surgery, radiation, and targeted drugs.
Why do I need follow-up for so many years if my tumor was removed? Because solitary fibrous tumor can come back or spread unusually late — sometimes a decade or more after the original treatment. A complete removal greatly lowers the risk, but it doesn't eliminate it entirely, especially for tumors with higher-risk features. Regular imaging over a long period means that if a recurrence appears at the original site, or a deposit shows up in the lungs, liver, or bone, it can be caught while it is small. Small, isolated recurrences can often be removed surgically or treated with focused high-dose radiation, so long-term surveillance directly improves the chance of keeping the disease controlled.
References
Numbered sources for the studies cited above. Links open the primary publication on PubMed or the publisher’s site.
- Molecular pathology studies defining the SFT/hemangiopericytoma spectrum (no indexed identifier — see your care team) ↩
- Postoperative radiotherapy outcome series in SFT (no indexed identifier — see your care team) ↩
- Antiangiogenic therapy trials in advanced SFT (no indexed identifier — see your care team) ↩