A desmoid tumor is an abnormal growth that arises from connective tissue, which is the tissue that provides strength and flexibility to structures such as bones, ligaments, and muscles. Typically, a single tumor develops, although some people have multiple tumors. The tumors can occur anywhere in the body. Tumors that form in the abdominal wall are called abdominal desmoid tumors; those that arise from the tissue that connects the abdominal organs are called intra-abdominal desmoid tumors; and tumors found in other regions of the body are called extra-abdominal desmoid tumors. Extra-abdominal tumors occur most often in the shoulders, upper arms, and upper legs.

Mutations in the CTNNB1 gene or the APC gene cause desmoid tumors. CTNNB1 gene mutations account for around 85 percent of sporadic desmoid tumors. APC gene mutations cause desmoid tumors associated with familial adenomatous polyposis as well as 10 to 15 percent of sporadic desmoid tumors. Both genes are involved in an important cell signaling pathway that controls the growth and division (proliferation) of cells and the process by which cells mature to carry out specific functions (differentiation).

Desmoid tumors are rare, affecting an estimated 1 to 2 per 500,000 people worldwide. In the United States, 900 to 1,500 new cases are diagnosed per year. Sporadic desmoid tumors are more common than those associated with familial adenomatous polyposis.

Most desmoid tumors are sporadic and are not inherited. Sporadic tumors result from gene mutations that occur during a person's lifetime, called somatic mutations. A somatic mutation in one copy of the gene is sufficient to cause the disorder. Somatic mutations in either the CTNNB1 or the APC gene can cause sporadic desmoid tumors.

Published Date: March 01, 2013
Published By: National Institutes of Health