Desmoid Tumor (NORD)

Desmoid tumors, also called aggressive fibromatosis, occur when connective tissue cells called myofibroblasts begin to multiply out of control, creating a tumor-like mass. The condition is similar to fibrosarcoma, a type of malignant cancer; however, desmoid tumors do not metastasize to other parts of the body. Given their cell of origin, they are part of a larger group of tumors called sarcomas.

Desmoid tumors are rare. The condition primarily affects young people, usually between 10 to 40 years of age, and is more common in females than males.

The pathology of desmoid tumors is currently not well known. In most patients, the disease occurs spontaneously, with no known specific trigger or cause. While estrogen or past surgeries in the same location as the tumor have been suggested as possible risk factors, more research needs to be done to confirm this.

That said, 3.5-32% of patients with familial adenomatous polyposis, an inherited syndrome where polyps develop in the intestine and skin, will develop desmoid tumors as part of this condition. These patients have a variant in their adenomatous polyposis coli, or APC gene, which is a tumor suppressor gene. The APC gene variant can cause uncontrolled cell division and, as a result, polyps develop within the patient’s body. Over time, if left untreated, these polyps can develop into tumors. Any patient who develops a desmoid tumor, particularly intra-abdominal, should be evaluated for this syndrome.

Symptoms vary from person to person, depending on the person’s age, where the tumor arises in the body, and the size of the tumor. The most common symptom is the development of a mass or swelling that is often painless to the touch. As the tumor gets bigger, the mass begins compressing the nerves and muscles around it, causing soreness or pain. This can lead to restricted movement or chronic limping if the tumor develops in the patient’s arms or legs. Tumors that arise in the bowels can cause abdominal pain or may lead to bowel obstruction or blockage if they get big enough.

Initial diagnosis is often done with medical imaging, through an ultrasound, CT scan, or MRI. The tumors are usually circumscribed, homogeneous masses with projections or tails. However, their appearance can be irregular and ill-defined particularly when they occur in the abdomen. The appearance and characteristics of these tumors are enhanced with injection of an intravenous contrast.

If a tumor is suspected, the diagnosis is confirmed through biopsy, where a small amount of tissue from the tumor is extracted and examined. Under a microscope, desmoid tumors characteristically have a high concentration of myofibroblasts, a cell that is typically seen during the late stages of wound healing. The nuclei of these cells often have an increased level of beta-catenin, a protein that is produced when someone has an APC gene variant. The tumor cells will also contain a number of antibodies, such as smooth muscle actin, desmin, and KIT.

Treatment depends on the size and location of the tumor, and the patient’s overall health. If the tumor is not causing significant symptoms, and the tumor growth is unlikely to compress important nearby structures, the first-line treatment is active surveillance, also known as "watch and wait." A third of all desmoid tumor patients see spontaneous regression of the tumor.

If the patient is experiencing significant symptoms, surgical removal, chemotherapy, radiation and ablative treatments may be used. The choice between these depends on the location of the tumor.