Desmoid tumors are slow-growing, mostly benign but locally aggressive tumors caused by the proliferation of fibroblasts. They are often associated with familial adenomatous polyposis and can arise from any part of the body, most commonly the extremities, abdominal wall, and the abdominal cavity. Individuals may be asymptomatic until the tumors grow large enough to compress adjacent structures (e.g., bowel obstruction). Diagnosis includes imaging and requires biopsy with immunohistochemistry for confirmation. Treatment is based on active surveillance with MRI.
- Rare (approx. 0.03 % of all tumors)
- Approx. 5–15 % are seen in association with familial adenomatous polyposis
- Peak incidence: 30–40 years of age 
- Sex: ♀ > ♂ (2:1) 
Epidemiological data refers to the US, unless otherwise specified.
- Beta-catenin/WNT (CTNNB1 gene) mutation: associated with sporadic development of desmoid tumors (∼ 85 %) 
- APC gene mutation: associated with familial adenomatous polyposis (FAP), specifically Gardner syndrome (∼ 15 %)
- Hyperestrogenic states (e.g., during or following a pregnancy, oral contraceptives use, IVF)
- Repeated trauma (e.g., surgical procedures)
According to etiology
According to location
- Located in the abdominal wall or rectus abdominis muscle
- Seen in Gardner syndrome and related to pregnancy
- Involves the intestinal mesentery or intrapelvic space
- Commonly seen in Gardner syndrome
- Involves the head and neck regions, thorax, breasts, shoulder girdle, and extremities
- Common in sporadic forms
Clinical findings may vary widely according to age, tumor size, and location.
- Painless mass
- Nerve or muscle compression may cause localized pain or tenderness
- Clinical features of bowel obstruction (e.g., abdominal pain, distention, nausea, vomiting)
Imaging: shows infiltration of muscles, deep tissue, and along muscle planes 
- Ultrasound: assessment of palpable masses
- MRI: assessment of tumors of the thorax, abdomen, head, neck, and extremities
- CT scan: assessment of intraabdominal desmoid tumors
Core needle biopsy (definitive diagnosis) 
- Histology: multiple fibroblasts with spindle cell morphology, numerous blood vessels, and poorly defined borders
- Immunohistochemistry: stain for vimentin, smooth muscle actin, and nuclear beta-catenin
- Molecular analysis: CTNNB1 or APC mutations
- Other: Colonoscopy and germline testing should be considered if FAP is suspected.
- Low-grade fibromyxoid sarcoma
- Gastrointestinal stromal tumors (GISTs)
- Sclerosing mesenteritis
- Retroperitoneal fibrosis (e.g., due to an underlying lymphoma)
The differential diagnoses listed here are not exhaustive.
- Active surveillance
- Pain management (NSAIDs)
Alternatives: Active treatment should be considered only in persistent progression.
- Surgical intervention: sporadic desmoid tumors localized in the abdominal wall
- Medical therapy: sporadic desmoid tumors localized at all other sites and for progressive FAP-associated desmoid tumors
- Antihormonal therapy (e.g., tamoxifen)
- Tyrosine kinase inhibitors (e.g., imatinib, nilotinib, sorafenib)
- Chemotherapy (e.g., low dose methotrexate plus vinblastine)
- Local ablative treatments (e.g., radiotherapy, cryotherapy): determined on an individual basis
- Desmoid tumors are locally aggressive and associated with a high local recurrence rate but lack metastatic potential.
- Unpredictable clinical course (from spontaneous regression to progression and stable chronic disease)
- Desmoid tumors may compress vital organs and disrupt their function with potentially fatal consequences.