Desmoid tumors, also known as aggressive fibromatosis, are rare noncancerous growths that can form in different parts of the body. If you have familial adenomatous polyposis (FAP), your risk of developing desmoid tumors is higher, but it doesn’t mean you’ll definitely get them.

This article will help you understand the connection between FAP and desmoid tumors, how FAP is diagnosed, and how it may affect your treatment options.

What Is Familial Adenomatous Polyposis?

In most cases, FAP is a genetic condition that is inherited. If you have FAP, it means there’s a mutation, or change, in a gene called APC. This gene normally helps control how cells grow and divide. A mutation in the APC gene can cause hundreds or even thousands of small growths, called polyps, to form in the colon and rectum. These polyps increase the risk of developing colorectal cancer. Over time, these polyps can turn into tumors or cancer if they’re not treated.

One of the key players in this process is a protein called beta-catenin. The APC gene helps regulate the levels of beta-catenin in your cells. When the APC gene is mutated, beta-catenin can build up in the cells because it’s not being properly controlled. The buildup of beta-catenin causes cells to grow and divide more, leading to the formation of polyps and, sometimes, desmoid tumors.

FAP is passed down through families. If one of your parents has it, there’s a 50 percent chance that you’ll get it, too. However, some people develop FAP without having any family history of the condition due to a spontaneous (random) mutation in the APC gene. This accounts for about 30 percent of people with FAP.

How Is FAP Diagnosed?

Because FAP is a genetic condition, it’s usually diagnosed through genetic testing. If you have a lot of polyps in your colon or if there’s a history of FAP in your family, your doctor might suggest you get tested for the APC mutation. It’s important to diagnose FAP early. This helps your care team catch potential issues, such as desmoid tumors or colon cancer, early — before they become more serious.

For desmoid tumors, doctors typically use imaging tests like magnetic resonance imaging (MRI) or computed tomography (CT) scans to see where the tumor is and how big it is. Sometimes, they’ll take a small sample of the tumor (a biopsy) to confirm that it’s a desmoid tumor and not something else.

If you or a loved one has FAP, regular checkups and screenings are important. Your doctor will probably recommend frequent colonoscopies (colon exams) to look for new polyps. They might also do other tests to keep an eye on your overall health and check for desmoid tumors.

The Connection Between FAP and Desmoid Tumors

If you have FAP, you’re more likely to develop desmoid tumors compared to people without the condition. Around 10 percent to 15 percent of people with FAP will get desmoid tumors at some point in their lives. Desmoid tumors can be more aggressive in people living with FAP, meaning they might grow faster or are more likely to come back after treatment. But just because you have FAP doesn’t mean you’ll develop a desmoid tumor.

Does FAP Influence Where Desmoid Tumors Show Up?

In people without FAP, desmoid tumors can appear anywhere in the body. But if you have FAP, tumors mostly appear as intra-abdominal tumors, meaning they grow into the abdomen and soft tissue surrounding the intestines.

The rest appear as extra-abdominal tumors, which can occur in other parts of the body, such as the arms, chest wall, legs, head, or neck. However, in people with FAP, the abdominal wall is also a common site for desmoid tumors. They can develop in the muscles and tissues that form the outer boundary of the abdomen, often near scars from previous surgeries.

How Does FAP Influence Treatment for Desmoid Tumors?

Treatment of desmoid tumors has changed a lot in recent years. Doctors used to rely more on surgery, but now they often recommend less invasive treatments first, especially for people with FAP.

Surgery

In the past, surgery was often the first step in treating desmoid tumors. But for people with FAP, surgery can be tricky. Abdominal tumors can be hard to remove completely, and surgery carries the risk of complications like bowel obstruction. Also, these tumors tend to come back after surgery. That’s why doctors are more cautious about recommending surgery for desmoid tumors unless it’s absolutely necessary.

Active Surveillance

A common practice for managing desmoid tumors is called active surveillance — also known as taking a “watch-and-wait” approach. If the tumor isn’t causing symptoms or growing very fast, your doctor will probably recommend taking this route first. This means keeping a close eye on the tumor with regular imaging scans to see if it changes over time. If the tumor remains stable and unproblematic, you might not need treatment right away.

Medications

There are several types of medications that can help shrink desmoid tumors or keep them from growing. In the past, nonsteroidal anti-inflammatory drugs (NSAIDs) were one such option, but they have fallen out of favor in recent years. They’re mostly used to relieve pain associated with the tumor.

Penn Medicine Abramson Cancer Center has found that desmoid tumors can sometimes be influenced by hormones like estrogen, especially in women. Hormone therapy involves using medications that block or lower the levels of these hormones. For example, in the past, antiestrogen drugs like tamoxifen were used to treat desmoid tumors. However, this approach is no longer widely used because hormonal therapies are not generally thought to improve the disease.

In recent years, newer drugs called tyrosine kinase inhibitors, like sorafenib (Nexavar), have shown promise in treating desmoid tumors. These medications work by blocking specific pathways that tumor cells use to grow and spread.

In November 2023, the U.S. Food and Drug Administration (FDA) approved nirogacestat (Ogisveo) — the first medication specifically for treating desmoid tumors. It works by stopping the enzyme gamma-secretase, a protein that plays a key role in starting the process that makes desmoid tumors grow. It’s a systemic (whole-body) treatment that can be beneficial for people with desmoid tumors that are growing quickly or causing a lot of symptoms.

Chemotherapy

Chemotherapy drugs work by targeting and killing rapidly dividing cells, including tumor cells. Chemotherapy is often used in cancer treatment and can also be effective in shrinking desmoid tumors that are resistant to other treatments. Drugs like methotrexate and doxorubicin are commonly used in the treatment of desmoid tumors. They can be used alone or in combination with other treatments and can be a good option for aggressive or quickly growing tumors.

Radiation Therapy

Radiation therapy (radiotherapy) isn’t used as often for desmoid tumors, but sometimes it’s necessary. This is partly because of the potential for long-term side effects, especially in younger people. But in some cases, it might be used in combination with other treatments, such as surgery, or if other treatments aren’t working.

Personalized Treatment Plans for FAP

Because FAP-related desmoid tumors can be aggressive, it’s important to have a personalized treatment plan. This means working with a team of specialists who understand both FAP and desmoid tumors. Together, they can help create a plan tailored to your specific needs. With this approach, they can focus on controlling the tumor, minimizing side effects, and improving your quality of life.

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 or familial adenomatous polyposis? How have these conditions affected your life? Share your experience in the comments below, or start a conversation by posting on your Activities page.