The only way to confirm you have a desmoid tumor (also called aggressive fibromatosis) is for your doctor to perform a biopsy. This test involves taking a tissue sample from the suspected tumor to look at more closely. It’s important to find a doctor and pathologist (tissue specialist) specially trained to recognize and diagnose desmoid tumors.

In this article, we’ll discuss what a biopsy is and why it’s an important part of your desmoid tumor diagnosis. We’ll also cover the importance of getting a second opinion to avoid receiving a misdiagnosis.

What To Expect During Your Biopsy

A biopsy can be an invasive procedure, depending on where your tumor is located. Desmoid tumors develop in the connective tissue found throughout your body. Common locations include:

• Intra-abdominal — In the tissues that provide blood vessels and support your intestines
• Abdominal wall — In the tissue that surrounds the organs in your abdomen
• Extra-abdominal — In soft tissues outside of the abdomen, like the chest wall, arms, legs, and shoulders

Your oncologist (cancer specialist) will use your imaging test results to confirm where to perform the biopsy. Desmoid tumors are typically found using computed tomography (CT) scans or magnetic resonance imaging (MRI). Once they find a suspected tumor, they’ll schedule your procedure.

Types of Biopsies

Your doctor will choose a biopsy technique based on where your tumor is located. The most common biopsy for diagnosing desmoid tumors is the core needle biopsy. This technique uses a hollow needle to take a “core” (column of tissue) from the tumor.

Another type — known as fine-needle aspiration — typically isn’t used to diagnose desmoid tumors. A fine-needle aspiration uses a thinner needle to take a smaller tissue sample. There’s a chance the doctor may not be able to find a tumor using this technique. This means you may not be diagnosed with a desmoid tumor even if you have one.

In some cases, your doctor may need to perform a more invasive biopsy to remove some or all of the suspicious tissue. An incisional biopsy involves making an incision (cut) in the tumor to remove a sample. An excisional biopsy removes the entire tumor during surgery.

Your health care team can help you weigh the pros and cons of different biopsies.

On the Day of Your Procedure

In most cases, you won’t need to prepare for a desmoid tumor biopsy. Your doctor may have you stop taking blood thinners before your procedure. Always ask your doctor before stopping any medications. If you’re having a biopsy taken from your abdomen, you may be asked to fast (no eating or drinking) on the day of your procedure.

Some biopsies are more invasive than others. Your doctor may offer sedation to help you relax. They’ll then numb the area with a local anesthetic where the needle will be inserted. Using your imaging test results, your doctor will guide the needle into the suspected tumor. They’ll take the tissue sample and send it to a pathologist. It may take a few days to get your results back.

After the biopsy is complete, a bandage is placed over the insertion site. It’s a good idea to rest for the remainder of the day. Be sure to keep the bandage in place as long as your doctor recommends. You may experience some pain and swelling in the biopsy area, but it should start feeling better within a few days.

Risks of Biopsy With Desmoid Tumors

When getting a biopsy for desmoid tumors, the main concerns are bleeding and pain. The risk depends on the type of biopsy: A fine-needle aspiration is usually less risky, while a surgical incisional biopsy can involve more pain and bleeding. After the procedure, your health care team will observe you for a while to make sure there is no bleeding and your pain is manageable.

The Role of a Pathologist

A pathologist is a doctor who specializes in looking at tissue samples to diagnose diseases. Some pathologists focus on looking at cells under a microscope to determine whether a person has cancer. It’s important to find a pathologist with experience diagnosing desmoid tumors.

The Desmoid Tumor Research Foundation recommends getting a diagnosis from a soft-tissue pathologist. They’re specially trained to look closely at desmoid tumor cells for specific signs of the disease. Other pathologists may not be as familiar with desmoid tumors because they’re very rare.

What Do Pathologists Look for in Desmoid Tumor Samples?

A soft tissue pathologist knows to look for specific changes in your cells. For example, some people with desmoid tumors may have changes in the size and shape of long, thin cells known as spindle cells. Others may have abnormal patterns in their skeletal muscle fibers.

Around 85 percent of sporadic tumors are caused by mutations (changes) in the CTNNB1 gene. Sporadic means the tumor is not caused by an inherited gene mutation. This gene provides instructions for the beta-catenin protein, which plays a role in sending growth signals in cells. Another 10 percent to 15 percent of sporadic tumors are caused by mutations in the adenomatous polyposis coli (APC) gene.

Pathologists can perform genetic testing on tissue samples to look for any gene mutations associated with desmoid tumors. These results help confirm your diagnosis and guide your doctor on which desmoid tumor treatments may be best for you.

Pathologists also use specialized stains to look for proteins in tissue samples. A soft-tissue pathologist can apply a special stain to the sample to see how much beta-catenin is in the cells. This test can help the pathologist make a diagnosis, but it doesn’t directly confirm that you have a desmoid tumor.

Why You Need a Biopsy To Diagnose Desmoid Tumors

A biopsy is the only way to confirm you have a desmoid tumor. A pathologist needs to look at cells from the tumor under a microscope to make a diagnosis. Your doctor also needs to rule out other diseases. Examples include:

• Other noncancerous growths in the soft tissue
• Cancer, including sarcomas (cancer in the soft tissues and bones)
• Muscle injuries
• Hematoma (a pool of clotted blood in a tissue or organ)

Each of these conditions requires a different treatment. If you’re misdiagnosed, you may not receive the treatment you need. This means your tumors could continue growing, and your condition could worsen over time.

Finding a Sarcoma Specialist

Desmoid tumors are often difficult to diagnose, especially for pathologists who have never seen them before. In the United States, only 900 to 1,500 people are diagnosed with desmoid tumors every year. This means your chances of receiving a misdiagnosis are higher.

If you have questions about your diagnosis, don’t be afraid to ask for a second opinion. Look for a sarcoma specialist if you’re not currently being treated by one. These doctors specialize in diagnosing and treating tumors in the soft tissues. You can ask your doctor to refer you to a specialist, or check the Sarcoma Alliance for Research Through Collaboration website for a sarcoma center near you.

Talk With Others Who Understand

MyDesmoidTumorTeam is the social network for people with desmoid tumors and their loved ones. On MyDesmoidTumorTeam, members come together to ask questions, give advice, and share their stories with others who understand life with desmoid tumors.

Have you had a biopsy to diagnose a desmoid tumor? Were you misdiagnosed with another condition? Did you find a soft tissue pathologist to confirm your diagnosis? Share your experience in the comments below, or start a conversation by posting on your Activities page.