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Desmoid tumor
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Conditions

Desmoid tumor

Desmoid tumors are rare, locally aggressive fibrous growths that do not metastasize but can recur, often driven by CTNNB1 or APC gene variants.

Overview

A desmoid tumor is an abnormal growth that arises from connective tissue, which provides strength and flexibility to structures such as bones, ligaments, and muscles. Affected individuals typically develop a single tumor, although some have multiple tumors. Desmoid tumors most often develop when people are in their 30s or 40s, but they can occur anytime between adolescence and late adulthood.

Classification by location:

  • Abdominal desmoid tumors: arise in the abdomen or abdominal wall.
  • Intra‑abdominal desmoid tumors: arise from the tissue that connects the abdominal organs.
  • Extra‑abdominal desmoid tumors: occur elsewhere, most often in the shoulders, upper arms, and upper legs.

Desmoid tumors are fibrous, much like scar tissue. They are generally noncancerous (benign) because they do not spread to other parts of the body; however, they can aggressively invade surrounding tissue and are often difficult to remove surgically. Recurrence is common, and in about 20 percent of cases the tumors shrink or disappear without treatment (spontaneous regression).

Symptoms

Desmoid tumors may be asymptomatic. When symptoms occur, the most common is pain, usually due to the tumor pressing against nearby organs, tissues, or blood vessels. Additional signs and symptoms depend on size and location:

  • Intra‑abdominal tumors can block the bowel, causing constipation.
  • Extra‑abdominal tumors can restrict joint movement, making it difficult to move the arms or legs.

Epidemiology

Desmoid tumors are rare, affecting an estimated 2 to 6 per 1 million people worldwide. In the United States, about 1,000 new cases are diagnosed each year. Approximately 10 percent of all desmoid tumors occur in people with familial adenomatous polyposis (FAP). Women develop desmoid tumors more often than men, accounting for about 70 percent of cases.

Causes & Risk Factors

Genetic variants drive most desmoid tumors:

  • Variants in the CTNNB1 gene account for around 90 percent of sporadic desmoid tumors.
  • Variants in the APC gene cause desmoid tumors associated with FAP.

Both genes are part of a cell‑signaling pathway that regulates cell proliferation and differentiation. CTNNB1 encodes beta‑catenin; pathogenic variants produce a stable beta‑catenin protein that accumulates in cells, leading to uncontrolled growth. The APC protein normally helps degrade beta‑catenin; APC variants produce a truncated protein that cannot form the degradation complex, also resulting in beta‑catenin accumulation.

Inheritance

  • Most desmoid tumors are not inherited; they arise from somatic (acquired) CTNNB1 variants.
  • FAP‑associated desmoid tumors result from an inherited (autosomal dominant) pathogenic variant in one copy of the APC gene.

Other Names

  • Aggressive fibromatosis
  • Desmoid fibromatosis
  • Desmoid‑type fibromatosis
  • Familial infiltrative fibromatosis
  • Hereditary desmoid disease
  • Musculoaponeurotic fibromatosis

Additional Information & Resources

Genetic Testing Information

  • Genetic Testing Registry: Desmoid disease, hereditary

Genetic and Rare Diseases Information Center

  • Desmoid tumor

Patient Support and Advocacy

  • National Organization for Rare Disorders (NORD)

Clinical Trials

  • ClinicalTrials.gov

Catalog of Genes and Diseases (OMIM)

  • DESMOID DISEASE, HEREDITARY; DESMD

Scientific Articles (PubMed)

  • PubMed

References

  • Cojocaru E, et al. Approach to screening for Familial Adenomatous Polyposis (FAP) in a cohort of 226 patients with Desmoid‑type Fibromatosis (DF): experience of a specialist center in the UK. Fam Cancer. 2022;21(1):69‑74. doi:10.1007/s10689-021-00230-8.
  • Escobar C, et al. Update on desmoid tumors. Ann Oncol. 2012;23(3):562‑569. doi:10.1093/annonc/mdr386.
  • Huss S, et al. beta‑catenin (CTNNB1) mutations and clinicopathological features of mesenteric desmoid‑type fibromatosis. Histopathology. 2013;62(2):294‑304. doi:10.1111/j.1365-2559.2012.04355.x.
  • Kasper B, et al. Current Management of Desmoid Tumors: A Review. JAMA Oncol. 2024;10(8):1121‑1128. doi:10.1001/jamaoncol.2024.1805.
  • Lips DJ, et al. The role of APC and beta‑catenin in the aetiology of aggressive fibromatosis (desmoid tumors). Eur J Surg Oncol. 2009;35(1):3‑10. doi:10.1016/j.ejso.2008.07.003.
  • Mangla A, et al. Desmoid Tumors: Current Perspective and Treatment. Curr Treat Options Oncol. 2024;25(2):161‑175. doi:10.1007/s11864-024-01177-5.
  • Riedel RF, Agulnik M. Evolving strategies for management of desmoid tumor. Cancer. 2022;128(16):3027‑3040. doi:10.1002/cncr.34332.
  • Trautmann M, et al. Novel pathogenic alterations in pediatric and adult desmoid‑type fibromatosis – A systematic analysis of 204 cases. Sci Rep. 2020;10(1):3368. doi:10.1038/s41598-020-60237-6.

Frequently Asked Questions

Even if a desmoid tumor is currently asymptomatic, you should seek medical attention if you notice any new or worsening symptoms. These can include increasing pain, a noticeable lump or mass that is growing, changes in bowel habits (like constipation if the tumor is intra-abdominal), restricted movement in a limb (if extra-abdominal), or any signs of pressure on nerves or blood vessels, such as numbness, tingling, or swelling.
Desmoid tumors are not considered cancer because they do not spread (metastasize) to distant parts of the body. However, they are locally aggressive, meaning they can grow into and damage surrounding tissues and organs, which can cause significant pain, dysfunction, or even be life-threatening depending on their location. This local aggressiveness makes them challenging to treat, often requiring treatments similar to those for some cancers, but their non-metastatic nature means the prognosis is generally better than for malignant cancers.
Treatment for desmoid tumors is highly individualized. Options can include watchful waiting (especially for asymptomatic or stable tumors, given the potential for spontaneous regression), surgery to remove the tumor, radiation therapy, or various medical therapies such as chemotherapy, targeted therapies, or hormone therapy. The choice of treatment depends on the tumor's size, location, symptoms, growth rate, and whether it has recurred. Due to the high recurrence rate, a multidisciplinary team approach is often used.
While most desmoid tumors occur sporadically (without a clear inherited cause), about 10% are associated with an inherited condition called familial adenomatous polyposis (FAP), which is caused by mutations in the APC gene. If your desmoid tumor is linked to an APC gene mutation or if there's a family history of FAP or multiple desmoid tumors, genetic counseling and testing for family members may be recommended to assess their risk.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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