Solitary Fibrous Tumor, from the CureRays guide library.

A solitary fibrous tumor is an uncommon growth of connective tissue — once called hemangiopericytoma — that most often arises around the lining of the lung or in the brain's coverings; most behave gently and are cured by surgery, but some can return or spread years later, so radiation is used to control disease that can't be fully removed and to lower the chance of it coming back.

What it is.

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.

How radiation treats it.

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 ways we can treat it.

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.

Questions we hear often.

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.

This guide is informational only. It is not medical advice — please confirm anything here with your care team.