Desmoid tumors, also called aggressive fibromatosis, are rare, non-cancerous growths that develop in the body’s connective tissues. Although they don’t spread to other parts of the body like cancer does, they can still cause serious problems because they grow into nearby muscles, nerves, and organs. This can lead to pain, limited movement, and other complications depending on where the tumor develops. 

Desmoid tumors are unpredictable—some grow quickly, others stay the same for years, and some even shrink without treatment. Because of this, treatment decisions are often made carefully, based on symptoms, tumor size, and location. This article explains what desmoid tumors are, their causes and symptoms, how they are diagnosed, and the latest treatment options available. 

Desmoid tumors are growths that form from fibroblasts—the cells responsible for making connective tissue. Even though they are technically benign, they tend to grow aggressively and can invade nearby tissue. Unlike cancers, they do not metastasize (spread to other organs). However, because they can grow back after treatment, they are considered locally aggressive. 

Desmoid tumors are classified by where they occur in the body: 

• Extra-abdominal desmoids: Found in the shoulders, chest wall, back, arms, or legs 

• Abdominal wall desmoids: Usually develop in the muscles of the abdomen 

• Intra-abdominal desmoids: Grow inside the abdomen, often in the mesentery (tissue that connects the intestines) 

Although rare, they account for less than 3% of all soft tissue tumors. 

Desmoid tumors are extremely rare, affecting about 2–4 people per million each year. They are most common in young adults between 15 and 40 years old and occur slightly more often in women. In people with FAP, the risk is much higher, especially for tumors inside the abdomen. 

Signs and symptoms of Desmoid Tumors 

Symptoms depend on where the tumor is located and how large it becomes. Some tumors cause no problems, while others lead to pain or restricted movement. 

Common symptoms include: 

• A firm, often painless lump or mass 

• Pain or tenderness around the area 

• Swelling or fullness 

• Restricted movement if the tumor is near a joint 

• Abdominal pain, bloating, or bowel issues (for intra-abdominal tumors) 

• Unexplained weight loss or fatigue in advanced cases 

Because symptoms can mimic other conditions, imaging and biopsy are needed to confirm the diagnosis. 

The exact reasons desmoid tumors develop are not fully clear, but experts know that genetics and hormones play major roles. Some people develop them without any clear trigger, while others inherit a tendency for them. Two main genetic mutations—CTNNB1 and APC—are closely linked to desmoid tumor formation. The CTNNB1 mutation is found in most random (sporadic) cases, while the APC mutation is seen in people with a genetic condition called familial adenomatous polyposis (FAP), which greatly increases the risk. 

Hormones, especially estrogen, also seem to influence tumor growth. Desmoid tumors often appear or enlarge during pregnancy and may shrink after menopause, suggesting that hormone levels affect their behavior. 

Other factors that may contribute include prior surgery or trauma to the affected area and a family history of FAP or Gardner syndrome. While these risks can raise the chances of developing a tumor, many people with desmoid tumors have no identifiable cause. 

The exact cause of desmoid tumors isn’t fully understood, but researchers know they are linked to genetic mutations and hormonal influences. Many cases appear to be random (sporadic), while others are inherited. 

Desmoid tumors begin when the body’s connective tissue cells, called fibroblasts, start multiplying out of control. Normally, fibroblasts help repair tissue after an injury, but in desmoid tumors, a genetic glitch keeps them growing when they shouldn’t. This happens because of a problem in the Wnt/β-catenin signaling pathway, a system that tells cells when to grow and when to stop. When the CTNNB1 or APC gene mutates, the signal gets stuck in the “on” position, leading to continuous growth of fibrous tissue. 

Although these tumors are not cancerous, they can still grow into nearby muscles, tendons, and organs. This local invasion can cause pain, swelling, or functional issues depending on where the tumor is located. In the abdomen, for example, a tumor might press on the intestines and lead to discomfort or bowel blockage. Because their behavior is unpredictable, doctors carefully monitor how each tumor grows before deciding on the best treatment plan. 

Symptoms depend on where the tumor is located and how large it becomes. Some tumors cause no problems, while others lead to pain or restricted movement. 

Common symptoms include: 

• A firm, often painless lump or mass 

• Pain or tenderness around the area 

• Swelling or fullness 

• Restricted movement if the tumor is near a joint 

• Abdominal pain, bloating, or bowel issues (for intra-abdominal tumors) 

• Unexplained weight loss or fatigue in advanced cases 

Because symptoms can mimic other conditions, imaging and biopsy are needed to confirm the diagnosis. 

Diagnosing desmoid tumors involves several steps: 

1. Clinical evaluation 

Your doctor will review your medical history, including any previous surgeries or family history of FAP, and perform a physical exam to check for lumps or tenderness. 

2. Imaging tests 

• MRI (Magnetic Resonance Imaging): The preferred imaging test. It helps determine the size and extent of the tumor. 

• CT scan: Useful for tumors inside the abdomen. 

• Ultrasound: Can detect more superficial tumors but is less effective for deeper ones. 

3. Biopsy 

A core needle biopsy confirms the diagnosis. The tissue sample is analyzed under a microscope, and immunohistochemistry is used to detect nuclear β-catenin—a hallmark of desmoid tumors. 

Desmoid tumors can resemble other soft tissue conditions, so doctors may need to rule out: 

• Fibrosarcoma 

• Neurofibroma 

• Nodular fasciitis 

• Low-grade fibromyxoid sarcoma 

• Scar tissue from previous surgery 

Treatment depends on the tumor’s location, symptoms, and rate of growth. Because some tumors stop growing or shrink on their own, immediate treatment isn’t always necessary. 

1. Active surveillance (“watchful waiting”) 

If the tumor isn’t causing symptoms, your doctor may recommend regular MRIs every 3–6 months to monitor growth. Many desmoid tumors remain stable or even shrink without intervention. 

2. Medication therapy 

• Anti-estrogen therapy: Drugs like tamoxifen or toremifene may slow growth, especially for hormone-sensitive tumors. 

• NSAIDs (e.g., sulindac, celecoxib): Can reduce inflammation and tumor size. 

• Chemotherapy: Used for rapidly growing or inoperable tumors (methotrexate, vinblastine, or doxorubicin-based treatments). 

• Targeted therapy: Tyrosine kinase inhibitors such as sorafenib, imatinib, or pazopanib can help control growth. 

• Experimental therapies: Drugs like gamma-secretase inhibitors (e.g., nirogacestat) and β-catenin inhibitors are being studied in clinical trials. 

3. Surgery 

Surgery may be an option when the tumor causes severe symptoms or threatens organ function. However, recurrence after surgery is common, so it is performed cautiously. 

4. Radiation therapy 

Used for tumors that can’t be removed surgically or don’t respond to medications. However, potential side effects (like tissue scarring) limit its use, especially in younger patients. 

Although desmoid tumors don’t spread to other parts of the body, they can cause serious local problems such as: 

• Chronic pain and limited mobility 

• Bowel obstruction or perforation (intra-abdominal tumors) 

• Nerve compression or vascular problems 

• Psychological stress and fatigue due to chronic disease 

Desmoid tumors rarely cause death, but they can significantly impact quality of life. Prognosis varies depending on tumor size, location, and genetic factors. Some tumors remain stable for years, while others may recur after treatment. Ongoing monitoring is crucial to catch any changes early. 

While desmoid tumors can’t always be prevented, certain steps can lower the risk in people with FAP or a family history of the condition: 

• Avoid unnecessary abdominal surgery, which can trigger tumor growth. 

• Undergo regular screening for desmoids if you have FAP. 

• Seek genetic counseling and APC mutation testing if there is a family history. 

• Discuss reproductive options like preimplantation genetic diagnosis with a specialist. 

Living with a desmoid tumor can be challenging, both physically and emotionally. Support from a multidisciplinary medical team—including oncologists, surgeons, pain specialists, and mental health professionals—can make a big difference. 

Coping tips: 

• Keep up with regular checkups and imaging. 

• Maintain a healthy lifestyle to improve overall well-being. 

• Seek support groups or counseling for emotional health. 

• Stay informed about clinical trials and emerging therapies. 

Desmoid tumors are rare, complex growths that require personalized care. Though not cancerous, they can behave aggressively and impact quality of life. Thanks to advances in understanding the genetic and hormonal drivers of these tumors, treatment has shifted from aggressive surgery to more conservative, targeted approaches. With proper management and follow-up, many people with desmoid tumors can live healthy, fulfilling lives. 

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