Why desmoid tumors are considered aggressive

Desmoid tumors are a rare type of benign tumor that form in fibrous connective tissues.

Also known as dense connective tissues, fibrous connective tissues are tissues that help provide structure, support, and protection for organs and other parts of the body. Examples include tendons, ligaments, the inner layer of the skin, the fascia (a type of tissue that wraps around muscles and organs), and aponeurosis (flat, interweaving sheets of connective tissue that function similar to tendons).

Because dense connective tissues are located throughout the body, desmoid tumors can occur in many locations. Common locations include the abdomen, neck, head, arms, and legs.

While desmoid tumors are benign, they are locally aggressive and behave differently than other types of benign tumors.

How do desmoid tumors occur?

To understand desmoid tumors and why they are considered benign-but-locally-aggressive, it helps to understand what tumors are and when they are considered cancerous.

All cells in the body follow a lifecycle, where they grow, divide, and expire on a set schedule. This schedule is regulated by genes, sections of DNA that provide cells with instructions for making proteins and other substances that make up cells and determine how cells function.

Sometimes genes undergo mutations that change how cells behave, including mutations that result in the unrestricted growth of cells. As cells continue to grow and multiply without restriction, they can form abnormal masses of tissue called tumors. Some tumors are cancerous, others are benign.

Desmoid tumors can occur in any tissue that contains cells called fibroblasts. Gene mutations cause these cells to grow in uncontrolled ways. Most cases are sporadic, meaning the genetic changes occur on their own with no definitive cause. Some cases occur alongside a type of colon cancer called familial adenomatous polyposis (FAP), which is caused by inherited genetics.

While desmoid tumors involve the uncontrolled growth of mutated cells, these tumors are not classified as cancerous. A defining feature of cancers is the ability to metastasize or spread to other areas of the body. Desmoid tumors do not metastasize.

Why desmoid tumors are considered aggressive

Tumors can be classified as benign or cancerous (malignant). Benign tumors remain in one location, do not typically invade nearby tissues, and do not spread to other parts of the body (though they can grow large in size and cause problems). Cancerous tumors can invade nearby tissues and metastasize (spread) to other locations in the body.

Desmoid tumors are considered benign because they remain in one location in the body and do not metastasize. However, desmoid tumors are considered locally aggressive and can invade nearby tissues and structures. Depending on where they occur, desmoid tumors can compress nerves, compress blood vessels, restrict joint movement, or press into the bowels or bladder.

Treatment for a desmoid tumor will depend on the location, size, and any problems the tumor is causing. For many years, surgery was the main treatment, but it is now used more selectively due to the potential for side effects, high rates of recurrence, and the availability of newer treatment options. In cases where a tumor is small or not causing problems, a healthcare team may recommend monitoring without treatment. In cases where treatment is required, medications are often the first treatment option, and medications may be used in combination with surgery or other procedures to destroy a tumor.