Desmoid tumor: A benign soft tissue tumor that occurs most often in young adults and involves the limbs or trunk but can also arise in the abdomen or thorax.

Desmoid tumors are benign. They never metastasize (spread to other parts of the body). However, they are very difficult to remove because they intertwine extensively with the surrounding tissues. These tumors look like dense scar tissue. Just like scar tissue, they adhere tenaciously to surrounding structures and organs.

Surgery has been the traditional main mode of therapy for desmoid tumors but up to 70% of desmoid tumors recur after surgery.

Radiation therapy has also been used to treat desmoid tumors. However, this exposes the patient to significant radiation with damage to surrounding tissues and puts them at risk for a cancer caused by the radiation (a secondary malignancy). Radiation also is hampered by a moderate recurrence rate.

The combination of surgery and radiation has also been used to treat these stubborn tumors. While somewhat successful, the combination of wide resection surgery and high dose radiation represents very aggressive treatment for a "benign" condition.

Limited (low dose) chemotherapy emerged in 1989 as a less aggressive treatment for desmoid tumors. The anti-tumor drugs are given in low doses, so there are minimal short-term and usually no long-term side effects.

Limited (low dose) chemotherapy causes one-third of desmoid tumors to vanish, one-third to shrink and the remaining third appear not to change, but they rarely progress and usually stop hurting.

Desmoid tumors are also called aggressive fibromatosis because they are locally aggressive and fibrous like scar tissue.