Desmoid tumors are noncancerous growths that occur in the connective tissue. Desmoid tumors most often occur in the abdomen, arms and legs.

Another term for desmoid tumors is aggressive fibromatosis.

Some desmoid tumors are slow growing and don't require immediate treatment. Others grow quickly and are treated with surgery, radiation therapy, chemotherapy or other drugs.

Desmoid tumors aren't considered cancers because they don't spread to other areas of the body. But they can be very aggressive, acting more like cancers and growing into nearby structures and organs. For this reason, people with desmoid tumors are often cared for by cancer doctors.


Desmoid tumor symptoms differ based on where the tumors occur. Desmoid tumors most often happen in the abdomen, arms and legs. But they can form anywhere in the body.

In general, signs and symptoms include:

  • A mass or area of swelling
  • Pain
  • Loss of function in the affected area
  • Cramping and nausea, when desmoid tumors occur in the abdomen

When to see a doctor

Make an appointment with your doctor if you have any persistent signs or symptoms that worry you.


It's not clear what causes desmoid tumors.

Doctors know these tumors form when a connective tissue cell develops changes in its DNA. A cell's DNA contains the instructions that tell a cell what to do. The changes tell the connective tissue cell to multiply rapidly, creating a mass of cells (tumor) that can invade and destroy healthy body tissue.

Risk factors

Factors that may increase the risk of desmoid tumors include:

  • Young adult age. Desmoid tumors tend to occur in younger adults in their 20s and 30s. This tumor is rare in children and older people.
  • A genetic syndrome that causes many colon polyps. People with familial adenomatous polyposis (FAP) have an increased risk of desmoid tumors. FAP is caused by a gene mutation that can be passed down from parents to children. It causes numerous growths (polyps) in the colon.
  • Pregnancy. Rarely, a desmoid tumor may develop during or soon after pregnancy.
  • Injury. A small number of desmoid tumors develop in people who've recently had an injury or surgery.