Overview
Desmoid tumors are growths made of cells that form in the body's connective tissue. A desmoid tumor also may be called desmoid-type fibromatosis or aggressive fibromatosis. These rare tumors most often grow in the belly, also called the abdomen, and in the lining of the belly. Other common places are the arms and legs. But desmoid tumors may happen anywhere in the body.
Desmoid tumors are not cancer. They cannot spread to other parts of the body. But they can grow aggressively into nearby tissues and organs, causing serious issues. Because of this, people with desmoid tumors often get care from specialists who treat soft tissue tumors, including cancer specialists.
Desmoid tumors can be confused with other soft tissue tumors. A biopsy and other tests are needed to diagnose desmoid tumors.
How a desmoid tumor grows and whether it needs treatment can be hard to predict. Some grow slowly. Many may not need treatment. Others grow more quickly. A desmoid tumor can grow into nearby organs or structures and cause symptoms. Most tumors are not life-threatening. But a desmoid tumor that grows in the head or neck can sometimes cause serious health issues.
Desmoid tumors may be treated with medicine, surgery or other options.
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Symptoms
Symptoms of a desmoid tumor depend on where the tumor is located. Desmoid tumors can develop anywhere in the body. Desmoid tumors most often form in the connective tissue of the wall of the belly, called the abdominal wall, arms and legs. These tumors rarely form in breast tissue.
Signs and symptoms of desmoid tumors typically include:
- A mass or area of swelling.
- Pain.
- Nausea and vomiting when a desmoid tumor grows in the belly.
If the desmoid tumor is close to the skin, you may see the mass or area of swelling. It may feel firm.
When to see a doctor
Make an appointment with a doctor or other healthcare professional if you have any ongoing symptoms that worry you.
Causes
It's not clear what causes desmoid tumors.
Desmoid tumors are growths of cells that form in the connective tissue. Connective tissue surrounds and supports other structures within the body.
Desmoid tumors happen when cells in the connective tissue develop changes in their DNA. A cell's DNA holds the instructions that tell the cell what to do. In healthy cells, DNA gives instructions for cells to grow and multiply at a set rate. The instructions also tell the cells to die at a set time. In tumor cells, the DNA changes give different instructions. The changes tell the tumor cells to make many more cells quickly. Tumor cells also can keep living when healthy cells would die. This causes too many cells within the connective tissue.
Some people notice they have a desmoid tumor after surgery or injury. Some people notice they have a desmoid tumor during or after pregnancy. It's not clear if these events lead to developing a desmoid tumor. There is no evidence that a diet or lifestyle factor causes or prevents a desmoid tumor. Diet and lifestyle also do not seem to affect tumor growth or need for treatment.
Risk factors
Anyone can develop desmoid tumors. But the risk of desmoid tumors can go up if you have a genetic syndrome that causes many colon polyps. People with a condition called familial adenomatous polyposis (FAP) have a higher risk of desmoid tumors. This genetic syndrome is caused by a genetic change that can be passed from parents to children. The inherited condition causes many growths, called polyps, in the colon. Most people with desmoid tumors do not have FAP.
Sept. 04, 2026