Desmoid tumors are rare, benign (noncancerous) tumors. They can develop anywhere in the body where there’s connective tissue and mainly appear in the arms, legs, and abdomen (stomach).

There are several health conditions related to desmoid tumor, also called aggressive fibromatosis. These include:

• Pregnancy
• Familial adenomatous polyposis (FAP)
• Gardner syndrome (a subtype of FAP)
• Colorectal (colon) cancer
• Physical trauma

Read on to learn more about these conditions and their potential connection to desmoid tumor.

1. Pregnancy

Desmoid tumors are sometimes related to pregnancy. These tumors generally develop in the stomach in the abdominal wall — more specifically, in the rectus abdominis muscle, which is the top layer of the “six-pack” muscles. Scientists think the tumors could be related to stretching of the abdominal wall or increase in estrogen levels that occur during pregnancy. Typically, pregnancy-related tumors are found about 18 to 24 months after delivery.

In general, symptoms of an abdominal desmoid tumor include:

• Swelling
• Pain
• Cramping
• Upset stomach and nausea

Desmoid tumors during pregnancy could also be related to a mother’s hormone changes. Sometimes, desmoid tumors will disappear on their own after a mother gives birth.

2. Familial Adenomatous Polyposis

People with FAP are predisposed to developing polyps (growths) in their colon and rectum. They have an inherited genetic mutation on the adenomatous polyposis coli (APC) gene, which contributes to tumor formation.

The APC gene helps to control cell division. FAP is an inherited condition, meaning you’re more likely to develop it if you have a family history of the disease. However, in 25 percent to 30 percent of FAP cases, the condition was caused by a spontaneous mutation of the APC gene.

Hundreds or even thousands of polyps may form in a person’s colon if they have FAP. If the polyps are not removed, the chances of one developing into colon or rectal cancer is near 100 percent. Talk to your doctor about monitoring your colon health if you or a relative has FAP or colorectal cancer.

In addition to the polyps, about 10 percent to 15 percent of people with FAP also develop desmoid tumors. The desmoid tumors are usually intra-abdominal, meaning they’re within the abdomen (80 percent). Other times, the tumors are found at the abdominal wall (10 percent to 15 percent). About 5 percent of the time, they’re extra-abdominal (located outside the abdominal wall).

Even though desmoid tumors are classified as benign (meaning they won’t spread to distant tissues), they’re still important to treat. Desmoid tumors are the second most common cause of death for people with FAP, behind colorectal cancer.

If your doctor thinks you may have FAP, they’ll probably recommend genetic testing and other diagnostic tests, such as:

• Digital rectal exam (feeling for abnormal bumps or inside your rectum)
• Colonoscopy (using a small, flexible camera inside your rectum and colon to look for polyps)
• Fecal blood tests (a lab test to check for blood in your stool)
• Colon X-ray exams (barium enema)

3. Gardner Syndrome

Gardner syndrome is a subtype of FAP. This is another rare, inherited condition where polyps form in the large and small intestines, in addition to the polyps in the colon and rectum. As with FAP, people with Gardner syndrome are very likely to develop colorectal cancer later in life.

Symptoms of Gardner syndrome include:

• Tooth abnormalities
• Bone growths
• Skin cysts
• Stomach pain

About 3 percent to 6 percent of people with Gardner syndrome have desmoid tumors. The tumors typically develop around surgical sites, in the mesentery (a membrane that holds the intestine to the stomach wall), or in the space behind the abdominal cavity.

One of the common treatments for FAP and Gardner syndrome is removing the colon to prevent colon cancer. For people with Gardner syndrome, desmoid tumors typically appear within three years of having colon surgery.

4. Colorectal Cancer

Colorectal cancer — also called colon cancer — usually starts as small polyps in the colon or rectum. People with FAP or Gardner syndrome often develop colon cancer later in life. Some treatments that can help treat colon cancer include:

• Surgery
• Radiation
• Chemotherapy
• Immunotherapy

Symptoms of colon cancer include:

• Diarrhea and upset stomach
• Bleeding in stool
• Cramping, bloating, gas
• Tiredness
• Rapid weight loss

Colon cancer without FAP or Gardner syndrome is not associated with desmoid tumor.

5. Physical Trauma

Desmoid tumors can form at past surgical sites or where the body has had blunt trauma. Examples include hernia repair, osteotomy (bone alignment), trauma from motor vehicle accidents, and skin-cancer removal.

Scientists think that the process of wound healing may cause desmoid tumors to form after trauma. Fibroblasts are cells that help to form connective tissue. Especially for people who have a mutation in the catenin beta 1 (CTNNB1) gene, the activity of fibroblasts may get disrupted. Fibroblasts stay in a “switched on” state, which can cause thick scars and the beginnings of desmoid tumors to form.

Some doctors choose to use robots during surgery to minimize trauma. For example, laparoscopic surgery uses a thin tube with a video camera to guide surgery, giving the patient two small holes instead of one large incision. However, studies show that laparoscopic surgery isn’t associated with lower rates of desmoid tumors. In fact, desmoid tumors are shown to form at both the site where the video camera was inserted and the larger surgical site where the instruments were inserted.

While surgery is a risk factor for developing a desmoid tumor, most people who undergo surgery do not develop one.

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.

Do you have a desmoid tumor and want to know more about conditions associated with desmoid tumors? Share your experience in the comments below, or start a conversation by posting on your Activities page.