Desmoid tumours are rare growths that form in the body’s connective tissue, creating challenges that can affect daily life, movement, and emotional wellbeing. Although these tumours don’t spread like cancer, they can grow aggressively into nearby structures, making them complex to manage and sometimes difficult to remove completely.
What Are Desmoid Tumours?
Desmoid tumours are noncancerous growths that develop in connective tissue, which is the material that provides support and structure to your body’s bones, muscles, ligaments, and organs. These tumours are also known by another medical term: aggressive fibromatosis. They grow from cells called fibroblasts, which normally help protect vital organs, provide structural support to tissues, and play an important role in healing wounds.[1][2]
While desmoid tumours are not classified as cancer because they do not spread to distant parts of the body, they can behave aggressively in a different way. They tend to invade nearby tissues and organs, growing into surrounding structures like muscles, nerves, and blood vessels. This local invasion can make them painful and difficult to treat. Some desmoid tumours grow very slowly, while others expand quickly and cause serious complications.[3][4]
These tumours can appear anywhere in the body where connective tissue exists, which is essentially everywhere. However, they most commonly develop in the abdomen, including the abdominal wall and the tissue surrounding the intestines. They also frequently form in the arms, legs, shoulders, upper thighs, and sometimes in the chest wall, head, or neck.[1][2]
How Common Are Desmoid Tumours?
Desmoid tumours are considered rare. Worldwide, only about two to six people per million are diagnosed with a desmoid tumour each year. In the United States, estimates suggest that up to 1,650 people receive this diagnosis annually. To put this in perspective, desmoid tumours represent only about three percent of all soft tissue tumours.[3][5][7]
Desmoid tumours can occur at any age, from adolescence through late adulthood, but they are most commonly diagnosed in people between the ages of 15 and 60. The majority of cases are found in young adults, particularly those between 20 and 44 years old. Women are diagnosed with desmoid tumours about two to three times more often than men, accounting for roughly 70 percent of cases. Many women are diagnosed during pregnancy or shortly after childbirth, and tumours in these cases often develop in the abdominal wall.[1][2][5][9]
What Causes Desmoid Tumours?
The exact cause of desmoid tumours remains unclear. Scientists know that these tumours form when connective tissue cells develop changes, or mutations, in their genetic material, which is called DNA. DNA contains the instructions that tell a cell how to function. When these instructions are altered, the cell may begin to multiply rapidly and form a mass of tissue, which becomes a tumour.[1][7]
Researchers have identified specific gene mutations that are commonly found in desmoid tumours. Around 90 percent of desmoid tumours that occur on their own, without a family history, involve changes in a gene called CTNNB1. This gene provides instructions for making a protein called beta-catenin, which helps control cell growth and division. When the gene is mutated, the beta-catenin protein becomes abnormally stable and does not break down when it should. It accumulates inside cells and continues to signal for cell growth, leading to the formation of a tumour.[9]
In cases where desmoid tumours occur as part of a hereditary condition called familial adenomatous polyposis (FAP), the cause involves mutations in a different gene, called APC. The protein produced by this gene normally helps regulate beta-catenin levels by forming a complex that breaks it down. When the APC gene is mutated, this process fails, and beta-catenin builds up, promoting uncontrolled cell growth.[9]
Who Is at Higher Risk?
Certain factors can increase the likelihood of developing a desmoid tumour. Young adults, particularly those in their 30s and 40s, are at higher risk compared to children or older adults. Being female also raises the risk, especially during or after pregnancy, when hormone levels change significantly. Some experts believe that high levels of the hormone estrogen during pregnancy may play a role in the development of desmoid tumours in the abdominal wall.[1][2]
People with familial adenomatous polyposis (FAP), a rare inherited condition that causes polyps to form in the colon, have a much higher risk of developing desmoid tumours. About 5 to 10 percent of people with FAP will develop desmoid tumours at some point in their lives. These tumours often appear at the site of previous surgery, such as where a colon polyp was removed. Some individuals with a specific form of FAP called Gardner syndrome face an even higher risk, with approximately 10 percent developing desmoid tumours.[2][4][5]
Physical trauma is another risk factor. Research shows that having a serious injury or being repeatedly injured in the same area of the body can increase the chances of a desmoid tumour forming in that location. Previous surgery or trauma to the abdomen has been linked to desmoid tumour development, and in one study, two-thirds of patients with desmoid tumours had a history of abdominal surgery.[2][4]
What Are the Symptoms?
Desmoid tumours do not always cause noticeable symptoms, especially if they are small or growing slowly. Many people only discover they have a desmoid tumour during an imaging test performed for another reason. However, when symptoms do occur, they depend largely on where the tumour is located and how large it has grown.[3][5]
The most common symptom is the presence of a visible or palpable lump or area of swelling, usually in the arms, legs, or abdomen. Pain is also a frequent complaint. This pain often occurs because the tumour presses against nearby nerves, organs, or blood vessels. Some people experience a tingling sensation or numbness in the affected area.[1][2]
When desmoid tumours develop in the abdomen or the tissue surrounding the intestines, they can cause digestive problems. Symptoms may include cramping, nausea, vomiting, constipation, or blockages in the bowel. People with abdominal tumours may also experience abdominal swelling, weight loss, or a general feeling of discomfort or malaise. In rare cases, abdominal desmoid tumours can cause muscle wasting.[1][5]
Desmoid tumours in the arms or legs can restrict movement and make it difficult to use the affected limb. They may cause deformity, weakness, muscle problems, or difficulty moving joints such as the shoulder, elbow, hip, or knee. This loss of function can interfere with daily activities and reduce quality of life. In some cases, tumours in the arms or legs also cause tiredness or fatigue.[5]
How Are Desmoid Tumours Diagnosed?
If a doctor suspects a desmoid tumour, the diagnostic process typically begins with a physical examination. The doctor will examine the area of concern and ask about your symptoms, medical history, and family history. This information helps guide the next steps in diagnosis.[5][11]
Imaging tests are an important part of the diagnostic process. The most common imaging techniques used are computed tomography (CT) scans and magnetic resonance imaging (MRI) scans. These tests create detailed pictures of the inside of your body, allowing doctors to see the location, size, and extent of the tumour. Imaging also helps doctors understand how the tumour is affecting nearby organs, blood vessels, and nerves. Ultrasound may also be used in some cases.[3][5][11]
To confirm the diagnosis, a biopsy is usually necessary. During a biopsy, a small sample of tissue is removed from the tumour and sent to a laboratory for analysis. A doctor called a pathologist examines the tissue under a microscope to determine the type of cells present and whether they match the characteristics of a desmoid tumour. The biopsy sample can be collected using a needle, which is less invasive, or through surgery, depending on the tumour’s location and other factors.[3][5][11]
Because desmoid tumours are rare, they can sometimes be misdiagnosed as other conditions. These include hypertrophic scars, keloids, low-grade sarcomas, gastrointestinal stromal tumours (GIST), or benign growths such as nodular fasciitis, lipomas, fibromas, schwannomas, or leiomyomas. Accurate diagnosis is essential for appropriate treatment.[5]
Can Desmoid Tumours Be Prevented?
There is no known way to prevent desmoid tumours entirely, as the exact cause is not fully understood. However, understanding risk factors can help with early detection and management. If you have a family history of familial adenomatous polyposis or have been diagnosed with FAP yourself, regular monitoring by a healthcare team is important. Genetic counseling and testing may be recommended for individuals with a family history of FAP or desmoid tumours.[9]
For people with FAP who require surgery to remove colon polyps or the colon itself, it is important to be aware that surgery can sometimes increase the risk of developing desmoid tumours at the surgical site. Discussing this risk with your healthcare provider before surgery can help with planning and monitoring.[5]
Avoiding repeated trauma or injury to the same area of the body may help reduce risk, although this is not always possible or practical. If you notice any unusual lumps, swelling, or persistent pain, seeking medical evaluation early can lead to timely diagnosis and treatment, which may improve outcomes.[2]
How Do Desmoid Tumours Affect the Body?
Desmoid tumours arise from fibroblasts, the cells that make up connective tissue. When these cells undergo genetic mutations, they begin to multiply uncontrollably, forming a dense, fibrous mass that resembles scar tissue. This mass, the desmoid tumour, does not have the ability to spread to distant parts of the body, which is why it is not considered a true cancer. However, it can be locally aggressive, meaning it invades and grows into the tissues immediately surrounding it.[1][3][4]
As a desmoid tumour grows, it can press on or grow into nearby structures such as muscles, blood vessels, nerves, and organs. This invasion can cause pain, restrict movement, and interfere with normal organ function. For example, a tumour in the abdomen can compress the intestines, leading to digestive problems or bowel blockages. A tumour in the arm or leg can grow into muscles and joints, limiting mobility and causing weakness.[5]
The behaviour of desmoid tumours is unpredictable. Some grow very slowly and remain stable for years, causing few or no symptoms. Others grow rapidly and become large, causing significant morbidity. In rare cases, desmoid tumours can shrink or even disappear on their own without treatment, a process known as spontaneous regression. This happens in about 20 percent of cases.[7][9][11]
One of the major challenges with desmoid tumours is their tendency to come back after treatment. Even after complete surgical removal, the tumour can recur in the same location. Recurrence rates vary widely, ranging from 15 percent to as high as 77 percent, depending on factors such as tumour location, size, surgical margins, and whether the patient has had previous surgery. Most recurrences happen within five years of treatment.[4][5]
The accumulation of beta-catenin protein inside tumour cells, caused by genetic mutations, is thought to be a key factor in the abnormal cell growth and invasion seen in desmoid tumours. This protein continues to signal for cell division and proliferation, allowing the tumour to grow and invade surrounding tissues. Understanding these molecular mechanisms has helped researchers develop targeted treatments that aim to block these signals and slow tumour growth.[9]
