Deep fibromatosis, aggressive fibromatosis, and desmoid-type fibromatosis — these are all names also given to desmoid tumors. They are all benign (noncancerous) growths that form in the soft, connective tissues, though the complex medical terms can be confusing. It’s true that desmoid tumors are a type of fibromatosis. However, there are key differences between these tumors and other types of fibromatosis.

In this article, we’ll cover the different types of fibromatosis and how desmoid tumors are similar and different. To learn more about fibromatosis and desmoid tumors, talk to your doctor.

What Is Fibromatosis?

Fibromatosis refers to an overgrowth of connective tissue that creates tumors or fibromas. These tumors are typically not cancerous. This means that they don’t metastasize (spread to other parts of the body). Fibromas are made from tough or fibrous tissues.

Types of Fibromatoses

Doctors typically divide fibromatoses into two groups — superficial and deep.

“Superficial” means the growths form near the surface of the skin, often in the hands, feet, or other areas just under the skin. These tumors are usually small, grow slowly over time, and tend to be less aggressive than deep fibromatoses, which develop deeper in the body and may affect muscles or organs.

Examples of superficial fibromatoses include:

• Dupuytren’s contracture — A condition that causes abnormally thick skin along the base of your fingers
• Knuckle pads — Abnormal skin growths on the finger or toe joints
• Dermatofibroma — Firm lumps of soft tissue that form underneath the skin

Desmoid tumors are a type of deep fibromatoses, which form inside the body. They can affect the muscles, organs, and bones. They can grow to large sizes and move inside nearby tissues. In some cases, desmoid tumors can block nerves and blood vessels. They can interfere with organ function and cause pain and discomfort.

You can also classify fibromatoses by age. Desmoid tumors are more common in adults, while superficial fibromatoses tend to occur more often in children.

Are Desmoid Tumors a Type of Fibromatosis?

Doctors classify desmoid tumors as a type of deep fibromatosis. The term “desmoid” comes from the Greek word “desmos,” which means “tendonlike.” This is because desmoid tumors look like tendons that connect muscles to bone.

What Causes Desmoid Tumors?

Researchers aren’t quite sure what causes desmoid tumors. They believe that some people develop mutations (variations) in their DNA over time. This is true for people with mutations in the CTNNB1 gene. This gene gives instructions for making a protein called beta-catenin. Cells use beta-catenin to grow and divide.

Mutations in the CTNNB1 gene prevent cells from breaking down beta-catenin. As more beta-catenin builds up inside the cells, the cells start growing uncontrollably. This eventually creates too much scar tissue and causes deep fibromatoses.

Other people have a genetic condition known as familial adenomatous polyposis (FAP). People with FAP have changes in the APC gene. FAP is associated with a higher risk of colon cancer and desmoid tumors.

Other reasons desmoid tumors develop include surgery, injury, and pregnancy. They all cause trauma that triggers the body’s wound-healing process. People with abnormal beta-catenin proteins can’t shut this process off. Eventually, scar tissue builds up and forms desmoid tumors.

Where Do Desmoid Tumors Form?

Unlike superficial fibromatoses, desmoid tumors tend to form deep within the body’s tissues. They include:

• Intra-abdominal desmoid tumors — Grow in the mesentery (tissue that covers the intestines)
• Abdominal wall desmoid tumors — Grow in the tissue wall that covers organs in the abdomen (belly)
• Extra-abdominal desmoid tumors — Grow outside the abdomen, typically in the chest, shoulders, arms, and legs

What Are Similarities and Differences Between the Types of Fibromatosis?

All fibromatoses develop in fibrous connective tissue. Research shows that both superficial fibromatoses and desmoid tumors have changes in growth signaling. These abnormal growths also look similar under a microscope. However, there are some key differences between the two.

Genetics

Desmoid tumors can involve mutations in the CTNNB1 and APC genes. People with superficial fibromatoses usually don’t have these changes. However, researchers have found high beta-catenin levels in cells from some superficial fibromatoses. This protein may be the reason superficial fibromatoses form. More research is needed to find out its exact role.

Studies show that superficial fibromatoses are also linked to genetics. Dupuytren’s contracture can be passed down through family members, but it can also develop randomly. Knuckle pads are also linked to genetic syndromes that affect the skin. Unlike desmoid tumors, there aren’t any specific genes that play a role in these superficial fibromatoses.

Growth and Treatment

Superficial fibromatoses stay where they grow. They rarely spread into other nearby tissues. If your doctor removes one, it likely won’t grow back.

On the other hand, desmoid tumors can be more aggressive. They can also grow very large. Some tumors reach inside tissues and continue growing. Surgery for desmoid tumors usually isn’t successful because the tumors often come back.

Instead of surgery, doctors typically use other approaches to shrink desmoid tumors. Treatment options can include:

• Chemotherapy
• Targeted biologic therapy
• Hormone therapy
• Radiation therapy
• Cryoablation

Many of these treatments also help manage malignant (cancerous) tumors. It’s important to note that desmoid tumors and fibromatoses don’t grow and spread like cancer.

Desmoid tumors may not need to be treated. Active surveillance, or periodic appointments to check for tumor growth, may be recommended instead.

Who Treats Fibromatoses?

Fibromatosis treatment depends on the type and location of your growth. People with superficial fibromatoses usually are treated by orthopedic doctors. This type of doctor specializes in treating bone and muscle diseases. For example, Dupuytren’s contracture treatment may require surgery to remove the abnormal connective tissue bands in the hand.

Desmoid tumors are rare tumors that many doctors likely haven’t seen. This makes it difficult to get an accurate diagnosis. Many people living with desmoid tumors are misdiagnosed at some point in their journey. The Desmoid Tumor Research Foundation recommends seeing a sarcoma specialist. A sarcoma specialist is an oncologist who focuses on treating soft tissue tumors like sarcomas (a type of cancer) or desmoid tumors.

Talk With Others Who Understand

On MyDesmoidTumorTeam, people share their experiences with desmoid tumors, get advice, and find support from others who understand.

Do you have questions about how desmoid tumors are a type of fibromatosis? Let others know in the comments below.