Extra-abdominal desmoids are deep-seated tumors that are rare and benign, meaning they do not spread to other parts of the body (metastasize).

Desmoid tumors are also called aggressive fibromatoses. They have this name because they are fibrous, similar to scar tissue, and can grow aggressively into surrounding muscle, tendons, joints, and even bone. They can reach significant sizes. Although they are typically slow growing, desmoids can at times grow rapidly, mimicking a malignant or cancerous process.

The exact cause of desmoid tumors is not known.

Tumors generally develop in just one area, but sometimes they may appear in several locations. Multiple locations of disease can be associated with familial adenomatous polyposis, a genetic abnormality in which potentially malignant polyps develop in the intestinal lining.

This supports the theory that desmoids have a genetic cause, but other theories have been explored - including hormonal and traumatic causes - with no definite conclusions.

Older children and young adults up to the age of 40 are most likely to have desmoid tumors. Extra-abdominal desmoids usually occur in men and are more common in the shoulder and buttock, followed by the back of the thigh and knee, the arm, and forearm.

The most common symptom is a mildly painful, firm mass or lump in an arm or leg.

At times the lesion may grow rapidly, causing pain and restricting motion in nearby joints. Although they are rarely fatal, desmoid tumors may invade local nerves and blood vessels. This can result in pain and marked disability.

A thorough physical exam is the first step in accurate diagnosis of desmoid tumors. Your doctor will assess the size and consistency of the lump, as well as its affect on the overlying skin, limb length, and motion of the surrounding joints.

A magnetic resonance imaging (MRI) scan gives your doctor information about the tumor. An MRI may show the overall size and location of the lesion and whether there is any involvement of surrounding vital structures.

A biopsy is necessary to confirm the diagnosis. During a biopsy, a tissue sample of the lesion is taken. The procedure can often be performed in the physician's office. This offers at least two advantages: the site of the incision is small and the diagnosis can be made more quickly.

Desmoid tumors are unpredictable. Some tumors grow at a rapid rate. This can cause concern for an underlying malignancy. Other tumors remain unchanged after diagnosis. There are even instances of spontaneous regression. This erratic behavior makes treatment challenging.

Treatment options vary. How a desmoid tumor is treated can depend upon the location of the tumor, its characteristics, and patient preferences.

After surgery, rehabilitation is geared toward strengthening muscles. The goal is to regain function and range of motion in the affected limb and surrounding joints. Patients often work with a physical therapist at first, who will develop a rehabilitation and exercise program. The program can be continued at home or at a local gym. Recovery time depends on the extent of the surgical procedure.

After treatment for a desmoid tumor, patients see their doctor on a regular basis. The doctor will monitor their progress and assess local recurrence. During the follow-up visits, the doctor will examine the area and may order tests, such as MRIs and/or CTs. If a long-term medication (hormonal therapy or NSAIDs) has been prescribed to treat the tumor, blood tests may also be ordered. Follow-up visits are scheduled every three months for two years, and then in 6 to 12 month intervals.

New research in the form of better drugs will likely be the mainstay for the treatment of desmoid tumors. Drugs such as IMATINIB show some early promise in desmoids management.