Desmoid tumors come from random genetic mutations (changes) — a surprise that you didn’t see coming. Imagine that everything in your body is working just fine, and then, out of nowhere, a small mistake in your DNA starts a domino effect. This process leads to the growth of these unusual tumors. However, certain conditions and factors raise your risk of developing desmoid tumors. Some of these risk factors are in your control, while others aren’t.

In this article, we’ll discuss six known causes and risk factors for desmoid tumors, also called aggressive fibromatosis. You can use this information to ask your doctor questions about your risk. Note that just because you have certain risk factors, it doesn’t guarantee you’ll develop a desmoid tumor.

1. Mutations in the CTNNB1 Gene

In most cases, desmoid tumors occur spontaneously, meaning there’s no clear cause. These are sometimes called sporadic desmoid tumors. These tumors develop from cells with somatic mutations — mutations a person gains during their lifetime. These mutations can’t be passed down from parents to their children.

The two most common somatic mutations that cause desmoid tumors are found in the catenin beta-1 (CTNNB1) gene or the APC gene. The CTNNB1 gene provides the instructions for making the protein beta-catenin. Around 85 percent of people with sporadic desmoid tumors have CTNNB1 mutations.

Beta-catenin is found in several types of cells throughout the body. It works alongside other proteins to tell cells when to grow and divide. When there’s a mutation in the CTNNB1 gene, it creates an abnormal beta-catenin protein that isn’t broken down when cells no longer need it. As a result, beta-catenin proteins accumulate in cells, telling them to grow and divide uncontrollably. This uncontrolled cell growth eventually leads to desmoid tumors.

2. Familial Adenomatous Polyposis

Around 5 percent to 10 percent of desmoid tumors are related to familial adenomatous polyposis (FAP). This inherited genetic condition causes hundreds of growths called polyps to form in your intestines. In the early stages of the disease, you may not experience any symptoms. As FAP gets worse, you may experience bloody stool, pain in your abdomen, diarrhea, or constipation.

FAP occurs in people with a mutation in the adenomatous polyposis coli (APC) gene. APC mutations are passed down through families, making it a hereditary condition. One type of FAP — known as Gardner syndrome — is associated with an increased risk of desmoid tumors.

People with FAP tend to develop intra-abdominal desmoid tumors. These growths occur in the tissue surrounding the intestines in the abdomen. Overall, desmoid tumors are found in 10 percent to 20 percent of those with FAP. Studies have also found that people living with FAP are 852 times as likely to develop desmoid tumors compared to the general population.

Because FAP is an inherited genetic condition, people with FAP who develop desmoid tumors have an inherited form of desmoid tumors. Be sure to let your doctor know if you have a family history of FAP, colorectal cancer, or colon polyps. You may be more likely to develop FAP or these conditions yourself.

If you’re diagnosed with FAP, your doctor will also recommend a colonoscopy to look for any new growths. A colonoscopy uses a camera attached to a long, thin tube to take pictures inside your intestines. You’ll also undergo genetic testing to see if your desmoid tumor is associated with FAP.

3. Biological Sex and Hormone Levels

Desmoid tumors are more common in females than males. Research from Desmoid Tumor Research Foundation shows that females are twice as likely to have desmoid tumors. This is because females have higher estrogen levels than males.

Desmoid tumor cells use estrogen to grow and divide. Cleveland Clinic has found that people with high estrogen levels — like females and pregnant individuals — tend to develop desmoid tumors more often. On the other hand, low estrogen levels caused by menopause can cause tumor shrinkage.

If you have a desmoid tumor, you’ll need to be careful about taking medications that contain estrogen. Examples include hormonal birth control and estrogen replacement therapy. Be sure to talk to your doctor about other treatment options.

Anti-estrogen medications have been used to treat desmoid tumors based on research showing that drugs like tamoxifen block desmoid tumor cells from using estrogen. However, based on newer research, this approach is no longer in favor.

4. Pregnancy

Women who are pregnant or have recently been pregnant are at a higher risk of developing desmoid tumors, per Cancer.Net. In fact, between 8 percent and 18 percent of desmoid tumor cases are caused by pregnancy. Studies show that these tumors typically develop in the abdominal wall muscles during the third trimester of pregnancy or shortly after giving birth.

Doctors believe that desmoid tumors develop from pregnancy for a few reasons. During pregnancy, the abdominal wall muscles stretch to make room for the growing fetus. This injury and trauma to the muscles can lead to desmoid tumors. Another reason why desmoid tumors develop during or after pregnancy is due to high estrogen levels.

If you have desmoid tumors and are thinking of conceiving, talk to your doctor about your risks — if you have a desmoid tumor, you may still be able to get pregnant. Your doctor will first need to confirm that your tumors aren’t in a region that could harm the fetus. They’ll also continue to monitor your tumors regularly if you become pregnant.

5. Injury or Surgery

Desmoid tumors can form in places where you previously had an injury or surgery. When you’re recovering from a trauma like surgery or a severe injury, your body triggers the wound-healing process. Specialized cells known as fibroblasts create scar tissue to close the wound. Once your body finishes healing, the fibroblasts turn off and go into a resting state.

In some people, the fibroblasts don’t turn off after healing a wound. They stay active and continue making scar tissue, which begins to build up. This tends to happen in people with mutations in the CTNNB1 gene. Eventually, the scar tissue creates desmoid tumors.

Although not all injuries or surgeries are preventable, careful monitoring after surgery is important if you’re at a higher risk for desmoid tumors.

Examples of injuries or surgeries that can lead to desmoid tumors include:

• Hernia repair (surgery that repairs weaknesses in the abdominal wall)
• Skin cancer removal
• Blunt-force trauma, such as an injury from a car accident
• Bone realignment surgery to correct alignment of or repair bones and joints

6. Age

Desmoid tumors can develop at any age but are more common in certain age groups. Most often, they are found in people who are between 15 and 60 years old, especially those in their 20s and 30s.

Remember that even if you’re outside of the “at-risk” range, you can still develop a desmoid tumor. If you notice a concerning mass or other symptoms associated with desmoid tumors, talk to your doctor. They can run tests to confirm your diagnosis and start you on the right treatment plan.

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.

Are you or a loved one living with a desmoid tumor? Do you have a certain condition or risk factor associated with desmoid tumors? Share your experience in the comments below, or start a conversation by posting on your Activities page.