Desmoids

Desmoids, also called desmoid tumors or aggressive fibromatosis, are rare clonal fibrous neoplasms arising from musculoaponeurotic structures. They are locally aggressive but do not metastasize. Histology shows an infiltrative spindle-cell proliferation in a collagenous stroma; many cases demonstrate nuclear beta-catenin positivity due to mutations in CTNNB1 or, in hereditary forms, APC.

Epidemiology and risk factors: the incidence is about 2–4 per million people per year, typically affecting young adults with a female predominance. A minority occur in patients with familial adenomatous polyposis (FAP). Desmoids can be associated with prior surgery, trauma, or pregnancy, and may arise de novo or in the setting of FAP.

Clinical features and sites: lesions are usually deep-seated and present as a firm, slow-growing mass. Symptoms depend on location and may include pain or functional impairment. Common sites include the abdominal wall, limbs, and intraabdominal region, with intraabdominal tumors more common in FAP.

Diagnosis: magnetic resonance imaging is preferred to define extent and relationships; computed tomography can help for intraabdominal disease. Definitive diagnosis requires biopsy showing an infiltrative spindle-cell proliferation. Immunohistochemistry typically reveals nuclear beta-catenin. CTNNB1 mutations are common in sporadic cases, while APC mutations are seen in FAP-associated tumors.

Management: treatment is individualized. Many desmoids are managed with active surveillance when asymptomatic or stable. When intervention is indicated, options include surgical resection with negative margins when feasible, radiotherapy for unresectable or recurrent disease, and systemic therapies such as NSAIDs or antiestrogen therapy, low-dose chemotherapy, and targeted agents (for example tyrosine kinase inhibitors) or experimental beta-catenin–pathway inhibitors.

Prognosis and follow-up: desmoids do not spread to distant sites but have a high rate of local recurrence after treatment, particularly intraabdominal tumors. Longitudinal imaging follow-up is common.