Desmoid Tumor: Diagnosis

Approved by the Cancer.Net Editorial Board, 11/2022

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 pictures of the inside of the body to see if the tumor has invaded nearby tissue or structures. 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.

How a desmoid tumor is diagnosed

There are different tests used for diagnosing a desmoid tumor. Not all tests described here will be used for every person. Your doctor may consider these factors when choosing a diagnostic test:

  • The suspected location of the tumor

  • Your signs and symptoms

  • Your age and general health

  • The results of earlier medical tests

Desmoid tumors are rare, and there are no standard screening tests for this type of 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. 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

Imaging tests show pictures of the inside of the body. 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. A radiologist is a medical doctor who uses imaging tests to help diagnose disease. 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 produces detailed images of the inside of the body using magnetic fields, not x-rays. 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 creates a picture using sound waves. 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 only way to make a definite diagnosis, even if other tests can suggest that cancer is present. During biopsy, a small amount of tissue is removed for examination under a microscope. A pathologist analyzes the sample(s). 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. This may also be called molecular testing of the tumor.

    (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 familial adenomatous polyposis (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 the results with you. If the diagnosis is a desmoid tumor, these results also help the doctor describe it. This is called staging.

If you are diagnosed with a desmoid tumor, it is important to learn if any other members of your family may have had desmoid tumors, colorectal cancer, or multiple colon polyps in the past. Approximately 10% to 20% of people with FAP, a genetic syndrome, develop a desmoid tumor (see Risk Factors). When planning treatment, doctors may recommend that certain patients have a colonoscopy to look for colon polyps or talk with a genetic counselor to learn whether their tumor is associated with FAP. If so, the syndrome may affect other family members as well, and specific genetic tests may be recommended for them. Learn more about genetic testing.

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.