Solitary fibrous tumour is a rare type of growth that can develop almost anywhere in the body, most commonly around the lungs, though it may also appear in the head, neck, abdomen, and other locations. These unusual tumours develop slowly and often go unnoticed for years until they grow large enough to cause discomfort or other symptoms.
Epidemiology
Solitary fibrous tumours, often abbreviated as SFTs, are extremely rare. They represent a very small fraction of all soft tissue growths, accounting for less than two percent of all soft tissue tumours that occur in the body. This rarity means that many healthcare professionals may encounter only a handful of cases throughout their entire careers.[2]
When looking at the bigger picture, the incidence of these tumours is estimated at approximately one to two new cases per million people each year. To put this in perspective, this means that in a country with a population of ten million people, only ten to twenty individuals would be diagnosed with a solitary fibrous tumour in any given year.[5][7]
In England specifically, an average of thirty-eight cases of solitary fibrous tumour are diagnosed every year. This small number reflects the truly uncommon nature of this condition and highlights why it remains relatively unknown outside of specialist medical circles.[4]
The disease does not appear to favour one gender over another, affecting both males and females equally. This is somewhat unusual in the world of tumours, where many conditions show a clear preference for one sex or the other. The equal distribution suggests that whatever causes these tumours to develop is not related to sex-specific factors such as hormones.[2][7]
Solitary fibrous tumours predominantly affect middle-aged and older adults. Most people who are diagnosed with this condition fall between the ages of forty and seventy years, with the median age at diagnosis being sixty-five years old. This means that half of all patients are diagnosed before age sixty-five and half after. While the tumours mainly affect older adults, they are most common in people who are between fifty and sixty years old.[2][4]
It is worth noting that solitary fibrous tumours are quite uncommon in children. When these growths do occur in younger individuals, they are considered particularly unusual and may require special attention from paediatric specialists.[2]
Causes
The exact reason why some people develop solitary fibrous tumours remains largely a mystery to medical researchers. Unlike many other conditions where clear risk factors such as smoking or exposure to certain chemicals have been identified, solitary fibrous tumours appear to develop without any obvious external triggers or lifestyle factors.[2]
Research has revealed that these tumours originate from cells in the body’s connective tissues, which are the tissues that support and connect other tissues and organs throughout the body. Connective tissues provide structure and help hold the body together, much like the framework of a building. When cells in these supporting tissues begin to grow abnormally, they can form the mass that becomes a solitary fibrous tumour.[1]
Scientists have discovered important clues at the genetic level that may help explain how these tumours develop. Research suggests that two specific genes, known as NAB2 and STAT6, may join together or fuse in an abnormal way. Both of these genes are normally located on chromosome twelve in the body’s genetic material. When these genes fuse together inappropriately, they create what scientists call a fusion gene.[2]
This genetic fusion appears to be a hallmark of solitary fibrous tumours. The NAB2-STAT6 fusion gene has been identified as a specific genetic signature that helps doctors confirm the diagnosis of these tumours. Scientists believe that this abnormal gene fusion may increase the risk of developing a solitary fibrous tumour, though they are still working to understand exactly how this genetic change leads to tumour formation.[5]
Some researchers think that solitary fibrous tumours occur when chromosomes in cells break and then rejoin in the wrong way. This incorrect rejoining could lead to the gene fusions that are seen in these tumours. However, scientists are still trying to determine why this chromosomal breaking and rejoining happens in the first place and whether this is the primary cause of tumour development or just one step in a more complex process.[4]
Risk Factors
Unlike many other diseases where specific risk factors such as smoking, diet, or exposure to certain substances are well established, solitary fibrous tumours do not have clearly identified risk factors that people can avoid. This can be frustrating for patients who naturally want to know why they developed this condition and whether they could have done anything to prevent it.
Age is the only demographic factor that appears to be associated with these tumours. Since most cases occur in people between the ages of forty and seventy, being in this age group could be considered a risk factor, though this is not something anyone can control. The tendency for these tumours to develop in older adults suggests that the cellular changes leading to tumour formation may accumulate over many years.[2]
The fact that these tumours affect males and females equally suggests that hormonal factors, which often play a role in gender-specific cancers, are not involved in the development of solitary fibrous tumours. Similarly, the lack of connection to known carcinogens or environmental exposures means that occupation, lifestyle choices, and geographic location do not appear to influence risk.[2]
Anyone can develop a solitary fibrous tumour regardless of their background, habits, or health history. This universality reinforces the understanding that these tumours arise from spontaneous genetic changes rather than from preventable causes. While this lack of identifiable risk factors can be unsettling, it also means that people who develop these tumours should not blame themselves or wonder what they could have done differently.
Symptoms
One of the most challenging aspects of solitary fibrous tumours is that they often grow silently for extended periods. These tumours tend to grow quite slowly, which means they may exist in the body for months or even years without causing any noticeable problems. In fact, up to half of all people with solitary fibrous tumours do not experience any symptoms at all. Their tumours are only discovered by accident when medical imaging is performed for an unrelated reason.[2]
When symptoms do occur, they typically only appear once the tumour has grown large enough to press on nearby organs, bones, or tissues. The specific symptoms a person experiences depend entirely on where the tumour is located in their body. This means that two people with solitary fibrous tumours in different locations may have completely different experiences.[2]
When a solitary fibrous tumour develops in or around the lungs and chest cavity, which is the most common location, it can cause several respiratory and chest-related symptoms. People may develop a persistent cough that does not go away with normal treatments. Some individuals experience chest pain that is not related to heart problems, a type of discomfort doctors call noncardiac chest pain. As the tumour grows and begins to press on the lungs or airways, shortness of breath, known medically as dyspnea, may develop. In some cases, people may cough up blood, which is always a concerning symptom that requires immediate medical attention.[1][2]
An unusual sign that can occur with chest tumours is something called clubbing of the fingers and toes. This refers to an enlargement of the fingertips and abnormal growth of the nails, making them appear rounded and bulbous. While clubbing can occur with various lung and heart conditions, its presence alongside other symptoms may prompt doctors to investigate further.[2]
When a solitary fibrous tumour forms in the abdomen, the symptoms are quite different from those affecting the chest. A swollen abdomen may be the first sign that something is wrong, as the growing tumour takes up space and pushes outward. People may experience difficulties with normal bodily functions, such as an inability to completely empty their bladder when urinating or constipation. Some individuals feel uncomfortably full even after eating only a small amount of food, a sensation that occurs because the tumour is taking up space that would normally accommodate digested food.[2][4]
Tumours in the head and neck area can cause a distinct set of problems. A blocked nose that does not clear may be one of the first signs. Some people experience changes in their voice, which occurs when a tumour presses on the structures involved in speech production. Nosebleeds can occur if the tumour affects blood vessels in the nasal area. In more severe cases, the tumour may affect vision or cause bulging of the eyes.[2][4]
When a solitary fibrous tumour develops in the soft tissue within the bony socket that holds the eyes, known as the orbit, it can significantly affect vision and eye function. People may notice that one eye appears to bulge forward, a condition called proptosis. Double vision, or diplopia, can occur when the tumour disrupts the normal positioning or movement of the eye. A drooping eyelid, called ptosis, may develop. Other symptoms include eye pain, reduced vision, swollen eyelids, and excessively watery eyes.[2]
In many cases, people may notice a lump or swelling in the soft tissue where the tumour is located. This lump is often slow-growing and typically painless, which is why it may be ignored for some time before medical attention is sought.[4]
A rare but important complication that can occur with larger solitary fibrous tumours is a condition called Doege-Potter syndrome. This unusual syndrome develops when the tumour releases a hormone that affects the body’s blood sugar levels. The result is low blood sugar, which can cause a range of symptoms including headaches, persistent tiredness, neurological problems such as confusion or difficulty concentrating, and an increased heart rate. In very rare instances, the hormones released by the tumour can cause excessive growth in certain parts of the body, leading to a condition called acromegaly.[4]
Prevention
Unfortunately, because the exact causes of solitary fibrous tumours remain unclear and no specific risk factors have been identified, there are no known prevention strategies for this condition. Unlike diseases where lifestyle modifications such as quitting smoking, improving diet, or increasing exercise can reduce risk, solitary fibrous tumours appear to develop spontaneously without connection to modifiable behaviours or exposures.
The genetic changes that seem to underlie these tumours, specifically the fusion of the NAB2 and STAT6 genes, appear to occur randomly. There is currently no way to prevent these genetic changes from happening or to detect them before a tumour develops. This means that even people who live extremely healthy lifestyles and avoid all known carcinogens can still develop a solitary fibrous tumour.
Since these tumours cannot be prevented, the focus shifts to early detection and prompt treatment once they do develop. This is particularly important because solitary fibrous tumours can sometimes come back after treatment or, in rare cases, spread to other parts of the body. Regular medical check-ups and being attentive to unusual symptoms, especially persistent lumps, unexplained breathing difficulties, or other concerning signs, can help ensure that these tumours are found and treated as early as possible.
Pathophysiology
Understanding how solitary fibrous tumours develop and grow at the cellular and molecular level helps explain their behaviour and the changes they cause in the body. These tumours are classified as mesenchymal neoplasms, which means they arise from mesenchymal cells. Mesenchymal cells are a type of cell found in connective tissues throughout the body, and they have the ability to develop into various types of supportive tissues including bone, cartilage, fat, and fibrous tissue.[3]
The defining feature of solitary fibrous tumours at the molecular level is the presence of an abnormal fusion between two genes: NAB2 and STAT6. This genetic fusion is now recognized as the hallmark of these tumours and is found in the vast majority of cases. The fusion creates a new, hybrid gene that produces an abnormal protein. This protein interferes with normal cellular regulation, leading to uncontrolled growth of fibroblastic cells, which are the cells that produce fibrous tissue.[5]
Scientists have developed a reliable way to identify this genetic abnormality using a laboratory technique called immunohistochemistry. This technique allows pathologists to detect the presence of STAT6 protein in the nucleus of tumour cells. When STAT6 is found in the cell nucleus rather than in other parts of the cell, it indicates that the NAB2-STAT6 fusion has occurred. This test has become an important diagnostic tool that helps doctors distinguish solitary fibrous tumours from other types of soft tissue growths that may look similar under the microscope.[5]
Most solitary fibrous tumours are benign, meaning they are not cancerous and do not spread to other parts of the body. However, the classification of these tumours is not as simple as just “benign” or “malignant.” Healthcare professionals now use a risk stratification system to categorize solitary fibrous tumours as low risk, intermediate risk, or high risk based on several factors. These factors include the patient’s age, the size of the tumour, and what the tumour cells look like under a microscope. This risk category helps predict how likely the tumour is to come back after treatment or to spread to other parts of the body.[1]
Even though most solitary fibrous tumours are noncancerous, about ten to thirty percent can show aggressive or malignant behaviour. This means they may invade nearby tissues, spread to distant parts of the body through a process called metastasis, or come back after they have been surgically removed. The potential for recurrence exists even many years after initial treatment, which is why long-term follow-up is essential for anyone who has had a solitary fibrous tumour.[5][7]
When solitary fibrous tumours do spread, they most commonly travel to the lungs, liver, and bones. The risk of metastasis can be as high as thirty-five to forty-five percent in some studies, and some research with longer follow-up periods has found even higher rates. This relatively high risk of spread, even from tumours that initially appear benign, explains why doctors recommend surgical removal of these tumours even when they are not causing symptoms.[5]
The tumours themselves are composed of fibrotic cells arranged in various patterns. When examined under a microscope, they typically show a characteristic appearance with fibrous and collagenous tissue. This dense, fibrous content is what gives these tumours their name. The tumours are usually well-defined with clear boundaries, and they often contain numerous blood vessels. This rich blood supply is why imaging studies often show intense enhancement when contrast material is injected during CT or MRI scans.[7]
The slow growth pattern of most solitary fibrous tumours reflects the relatively stable nature of the abnormal cells. Unlike rapidly dividing cancer cells, the cells in most solitary fibrous tumours multiply at a measured pace. This slow growth explains why these tumours can be present for years without causing symptoms or being detected. It also contributes to the generally favourable prognosis for many patients, as slow-growing tumours are often easier to manage with surgical removal.
However, there is a subset of solitary fibrous tumours that behave very differently. These more aggressive tumours, sometimes called dedifferentiated solitary fibrous tumours, grow much faster and are more likely to spread. They represent the high-risk category and require more aggressive treatment approaches. Understanding which category a particular tumour falls into is crucial for determining the best treatment strategy and predicting outcomes.[5]
