Desmoid Tumor: Diagnosis

Approved by the Cancer.Net Editorial Board, 07/2020

ON THIS PAGE: You will find a list of common tests, procedures, and scans that doctors use to find the cause of a medical problem. Use the menu to see other pages.

Doctors use many tests to find, or diagnose, a desmoid tumor. They also do tests to see the tumor’s size and learn if the tumor is growing. For example, imaging tests can show if the tumor has invaded nearby tissue or structures. Imaging tests show pictures of the inside of the body. Doctors may also do tests to learn which treatments may work best.

For most types of tumors, a biopsy is the only sure way for the doctor to know if an area of the body has a tumor. In a biopsy, the doctor takes a small sample of tissue for testing in a laboratory. If a biopsy is not possible, the doctor may suggest other tests that will help make a diagnosis. Although biopsies have a small chance of not giving a definite answer, they are very important to allow your doctor make a clear diagnosis and develop a clear, comprehensive treatment plan.

This section describes options for diagnosing a desmoid tumor. Not all tests listed below will be used for every person. Your doctor may consider these factors when choosing a diagnostic test:

  • The suspected location of your tumor

  • Your signs and symptoms

  • Your age and general health

  • The results of earlier medical tests

There are no standard screening tests for a desmoid tumor. A doctor should examine any unusual or new lumps or bumps that are growing or are larger than 2 inches. Desmoid tumors can have no symptoms and grow in the body for many months or years before they are diagnosed. A tumor also may be found unexpectedly when people have imaging procedures done for reasons unrelated to the tumor. Desmoid tumors are rare. If a desmoid tumor is suspected, it is very important to talk with a doctor who has experience with this type of tumor.

A diagnosis of a desmoid tumor is made by a combination of clinical examination by a doctor and imaging tests. It is confirmed by the results of a biopsy. In addition to a physical examination, some of the tests described below may be used to diagnose a desmoid tumor.

Imaging tests

Radiologists will use the way the tumor looks on imaging tests to help determine whether it may be a desmoid tumor; however, a biopsy is almost always needed as well. If a desmoid tumor is suspected, it is important to have a radiologist experienced in reviewing the imaging scans of desmoid tumors. If possible, the same type of imaging test and the same radiologist should review all subsequent scans so that tumor size measurements are consistent.

  • Magnetic resonance imaging (MRI). An MRI uses magnetic fields, not x-rays, to produce detailed images of the body. MRI can be used to measure the tumor’s size. A special dye called “contrast” is given before the scan to create a clearer picture. This dye is injected into a patient’s vein. An MRI is the recommended imaging test for abdominal wall and extra-abdominal desmoid tumors. It is also used to look for a recurrence of the tumor after surgery.

  • Computed tomography (CT or CAT) scan. A CT scan takes pictures of the inside of the body using x-rays taken from different angles. A computer combines these pictures into a detailed, 3-dimensional image that shows any abnormalities or tumors. A CT scan can be used to measure the tumor’s size. Sometimes, a special dye called contrast medium is given before the scan to provide better detail on the image. This dye can be injected into a patient’s vein and/or be a pill or liquid the patient must drink. CT scans with contrast are often recommended for diagnosing intra-abdominal tumors.

  • Ultrasound. An ultrasound uses sound waves to create a picture. It may be used to look at lumps under the skin or other organs in the body.


Imaging tests may suggest the diagnosis of a desmoid tumor, but a biopsy is needed to confirm the diagnosis. It is very important for a patient to see a desmoid tumor specialist before any surgery or biopsy is done.

  • Biopsy. A biopsy is the removal of a small amount of tissue for examination under a microscope. Other tests can suggest that the tumor is present, but only a biopsy can make a reliable diagnosis. A pathologist is a doctor who specializes in interpreting laboratory tests and evaluating cells, tissues, and organs to diagnose disease.

    Because desmoid tumors are uncommon and can be misdiagnosed, an expert sarcoma pathologist should review the tissue sample to properly diagnose the tumor. Properly diagnosing a desmoid tumor requires special tests on the tumor tissue, and it is best if a specialist familiar with this type of tumor does this.

    There are different types of biopsies. The type that is done depends on the location of the tumor. For a needle biopsy, a doctor removes a small sample of tissue from the tumor with a needle-like instrument—usually a core needle biopsy. Fine needle aspirations are not recommended because they do not reliably find desmoid tumors. The biopsy may be performed with the help of ultrasound, CT scan, or MRI (see “Imaging tests,” above) to precisely guide the needle into the tumor. In an incisional biopsy, a surgeon cuts into the tumor and removes a sample of tissue. In an excisional biopsy, the surgeon removes the entire tumor. Because desmoid tumors frequently recur after surgery (see Types of Treatments), it is important to talk with your doctor about the potential benefits and risks of this type of biopsy with your doctor.

    The type of biopsy and how it is done are important in diagnosing and treating desmoid tumors, so patients should be seen in a sarcoma specialty center even before the biopsy is performed.

  • Tissue testing of the tumor. Your doctor or the pathologist looking at the tumor may recommend running laboratory tests on a tumor sample to identify specific genes, proteins, and other factors unique to the tumor. Beta-catenin (CTNNB1) gene mutations occur in 85% of desmoid tumors that are sporadic. This means the mutation is acquired during a patient’s lifetime and is not inherited. Mutations in the adenomatous polyposis coli (APC) gene cause 10% to 15% of sporadic desmoid tumors. In addition, inherited mutations in the APC gene can cause desmoid tumors associated with FAP (see Risk Factors). Results of laboratory tests that screen for CTNNB1 and/or APC mutations can help confirm a desmoid tumor diagnosis and may help determine what the treatment should be (see Types of Treatment).

After diagnostic tests are done, your doctor will review all of the results with you. If the diagnosis is a desmoid tumor, these results also help the doctor describe it. This is called staging.

The next section in this guide is Stages. It explains the system doctors use to describe the extent of the disease. Use the menu to choose a different section to read in this guide.