Solitary Fibrous Tumour

SFT, pleural solitary fibrous tumors, benign fibrous tumors of the pleura

Solitary fibrous tumours are rare growths that can develop almost anywhere in the body, most commonly around the lungs. While they usually grow slowly and may not cause symptoms for years, understanding these tumours is important for proper diagnosis and treatment.

Table of contents

• What is a solitary fibrous tumour?
• Where solitary fibrous tumours occur
• Who is affected
• Causes and genetic changes
• Signs and symptoms
• How solitary fibrous tumours are diagnosed
• Treatment options
• Risk categories and outlook

What is a solitary fibrous tumour?

Solitary fibrous tumours are growths of cells that start from tissues that support other tissues in the body, known as connective tissues^[1]. These tumours are classified as a type of soft tissue tumour, which means they develop in the soft parts of the body rather than in bones^[2].

Solitary fibrous tumours are quite rare. They account for less than 2% of all soft tissue tumours^[2]. In England, an average of only 38 cases are diagnosed each year^[4].

Most solitary fibrous tumours are not cancerous, meaning they grow slowly and do not spread to other parts of the body. However, some can become cancerous and may spread or come back after treatment^[2]. Even when tumours are not cancerous, healthcare providers usually recommend surgery or another treatment to remove them^[2].

Where solitary fibrous tumours occur

• Pleura (lining around the outside of the lungs)
• Head and neck
• Abdomen
• Breast
• Kidney
• Prostate
• Spinal cord
• Connective tissue surrounding brain and spinal cord
• Liver
• Paranasal sinuses inside the nose
• Soft tissue within the eye socket (orbit)
• Thyroid

Solitary fibrous tumours can form in almost any part of the body^[1]. The most common location is in the lining around the outside of the lungs, called the pleura. When tumours occur in this area, they are called pleural solitary fibrous tumours^[1].

In terms of where these tumours develop across the body, about 30% occur in the pleural area, 27% in the tissue surrounding the brain and spinal cord (meninges), 20% in the abdomen and pelvis, and the rest in other locations^[7].

Who is affected

Solitary fibrous tumours mainly affect older adults. They are most common in people who are 50 to 60 years old^[2]. The median age at diagnosis is 65 years old^[4]. These tumours can affect both males and females equally^[4].

Solitary fibrous tumours are uncommon in children^[2]. Anyone can develop these tumours, but they tend to affect middle-aged or older people between the ages of 40 and 70 years old^[4].

Causes and genetic changes

Experts are not sure why some people develop solitary fibrous tumours^[2]. Unlike some other tumours, solitary fibrous tumours are not related to asbestos exposure^[2].

Research suggests that two genes—NAB2 and STAT6—may join or fuse together. This fused gene or gene change may increase the risk of developing a solitary fibrous tumour^[2]. Scientists think that solitary fibrous tumours occur when chromosomes in cells break and re-join in the wrong way^[4]. Researchers are still trying to find out why this happens and whether this causes the tumours^[4].

The identification of the NAB2-STAT6 fusion gene has emerged as a specific marker for solitary fibrous tumours^[5]. This discovery has helped doctors better understand and diagnose these tumours.

Signs and symptoms

Solitary fibrous tumours tend to grow slowly. They might not cause symptoms until they grow large^[1]. Up to half of people with solitary fibrous tumours do not have any symptoms at all^[2]. Symptoms may only occur once the tumour gets large and presses on nearby organs, bones or tissues^[2].

When symptoms do occur, they vary depending on which part of the body the tumour affects^[1]. Before receiving a diagnosis, a person may experience all, some, or none of these symptoms^[4].

A common symptom across different locations is a lump or swelling in the soft tissue. This lump is often slow-growing and painless^[4].

Symptoms in or around the lungs

When a solitary fibrous tumour develops in the chest cavity, including the pleura and lungs, symptoms may include^[1][2]:

• Chest pain
• Chronic cough or coughing
• Coughing up blood
• Shortness of breath
• Swelling of fingers or toes
• Clubbed fingers and nails (enlarged fingertips and unusual growth of nails)

Symptoms in the abdomen

If the tumour is in the abdomen, a person may experience^[4]:

• A swollen abdomen
• An inability to completely empty the bladder when urinating
• Constipation
• A feeling of being very full even after only eating a small amount of food

Symptoms in the head and neck area

Symptoms in the head and neck area may include^[4]:

• A blocked nose
• Changes in voice
• Nosebleeds

Symptoms affecting the eyes

When a solitary fibrous tumour occurs in the soft tissue within the eye socket (orbit), it can affect vision, causing^[2]:

• Bulging eyes
• Double vision
• Drooping eyelid
• Eye pain
• Low vision
• Swollen eyelids
• Watery eyes

Doege-Potter syndrome

Some larger solitary fibrous tumours are known to release a hormone which can cause a condition called Doege-Potter syndrome^[4]. This syndrome can cause signs and symptoms such as:

• Low blood sugar, which can result in headaches, tiredness, neurological problems, and an increased heart rate
• Rarely, increased growth in certain parts of the body due to a condition called acromegaly

How solitary fibrous tumours are diagnosed

Diagnosis of solitary fibrous tumours often requires a comprehensive approach involving several different types of tests^[3]. A specialist doctor will diagnose a solitary fibrous tumour through a series of tests^[4].

The diagnostic process typically includes^[4]:

Physical examination: The doctor will look at and feel any lump that is present.

Imaging scans: These tests take pictures of the inside of the body. Common scans include CT (computed tomography) scans or MRI (magnetic resonance imaging) scans^[4]. These imaging studies help doctors see the size, location, and characteristics of the tumour.

Biopsy: This involves taking and testing a sample of the tumour^[4]. A biopsy is when a small piece of tissue is removed from the body so it can be examined under a microscope. Using this biopsy, a doctor will look to see if the sample looks like a solitary fibrous tumour and whether it contains the chromosome error associated with these tumours^[4].

The identification of STAT6 nuclear protein expression and the NAB2-STAT6 fusion gene has become an important tool for accurate diagnosis of solitary fibrous tumours^[5]. These molecular and immunohistochemical (a laboratory method that uses antibodies to check for certain markers in tissue samples) assessments help differentiate solitary fibrous tumours from other soft tissue tumours^[3].

Treatment options

Treatment for solitary fibrous tumours typically involves several approaches, with surgery being the most common first option.

Surgery

The first treatment method for solitary fibrous tumours is surgery^[4]. Treatment often involves surgery to remove the tumour^[1]. The surgeon will remove the tumour and will aim to take out an area of normal tissue too, which is called “taking a margin”^[4]. This is done to make sure the surgeon removes all the cancer cells.

If a solitary fibrous tumour is affecting the arms and legs, surgeons will do limb-sparing surgery so the limb can continue to work well^[4]. If the cancer has spread throughout the limb, surgeons may have to perform a partial or full amputation, but this is very rare^[4].

Radiotherapy

This treatment uses high-energy radiation to destroy cancer cells^[4]. A person may have radiotherapy either before or after surgery^[4]. Radiation therapy may be considered in cases of tumours that cannot be removed by surgery or that have spread^[3].

Other treatments

Additional treatment options may include chemotherapy and targeted therapy^[2]. These treatments might be considered for tumours that cannot be removed by surgery or for those that have spread to other parts of the body^[3].

Risk categories and outlook

Healthcare professionals assign solitary fibrous tumours a risk category that indicates how likely they are to come back after treatment or spread to other parts of the body^[1]. Solitary fibrous tumours can be classified as low, intermediate, or high risk^[1].

The risk category is based on different factors such as the patient’s age, the size of the tumour, and what the tumour looks like under a microscope^[1]. In recent medical classifications, risk stratification models have been recommended as better tools to determine outlook in solitary fibrous tumours^[5].

Sometimes the tumour comes back after surgery or spreads to other parts of the body^[1]. The risk for the tumour spreading to other parts of the body (metastasis) can be up to 35-45%, or even greater in studies with longer follow-up periods^[5]. About 10-30% of solitary fibrous tumours show aggressive or malignant behaviour such as local invasion, distant spread, and recurrence^[7].

Long-term follow-up is essential due to the potential for late recurrences and spread of the disease^[3]. This underscores the importance of continued monitoring in managing patients with solitary fibrous tumours^[3].