Synonyms

• Desmoid tumour
• deep fibromatosis
• aggressive fibromatosis

Category

Soft tissue

Behaviour

Intermediate

Gender

Female

Tissue of Origin

Fibrous

Epidemiology

• Incidence 2–4 per million per year
• Peak incidence in reproductive-age women
• Associated with FAP (familial adenomatous polyposis) in 5–10%
• May be sporadic, post-traumatic, or hormonal

Clinical Features

• Firm, painless or mildly painful deep soft tissue mass
• Progressive growth causing restriction and pain
• Intestinal desmoids in FAP: obstruction, perforation
• Spontaneous regression documented in 20–30%

Location

• Abdominal wall (post-pregnancy most common)
• Intra-abdominal (mesenteric) especially in FAP
• Extra-abdominal: shoulder girdle, chest wall, limbs, head and neck

Imaging

• Well-defined to infiltrative hypointense mass on T1 MRI
• Variable T2 signal (Low in Fibrous areas, High in myxoid areas)
• Enhancement patterns Variable
• CT: Low-density soft tissue mass

Pathology

• Bland spindle cells in abundant collagenous stroma
• Low cellularity, rare mitoses, no necrosis
• Nuclear beta-catenin positivity (IHC)
• CTNNB1 mutation or APC mutation

Genetics

• Sporadic: CTNNB1 (beta-catenin) somatic mutation in 85%
• FAP-associated: APC germline mutation
• T41A, S45F, S45P mutations associated with worse recurrence risk
• No recurrent chromosomal alterations

Treatment

• Active surveillance (watch and wait) - first-line for asymptomatic stable lesions
• Sorafenib or pazopanib - most active systemic agents
• Imatinib - activity in PDGFR-expressing tumours
• Surgery - reserved for symptomatic/progressive lesions with achievable clear margins; High recurrence rate
• Radiotherapy for unresectable or recurrent disease

Prognosis

• No Malignant potential - does not metastasise
• Local recurrence remains the major problem (30–70% after surgery)
• Spontaneous regression in 20–30% - supports watchful waiting
• FAP-associated intra-abdominal desmoids: Higher morbidity and mortality

Key Points

• Watch-and-wait is now first-line management for most asymptomatic lesions
• CTNNB1 mutation type predicts recurrence risk
• Screen for FAP when intra-abdominal/mesenteric desmoid is diagnosed
• Sorafenib is currently the most active systemic treatment based on RCT data

Workup - Blood Tests

• FBC, U&E, LFTs - baseline
• CTNNB1 mutational status from biopsy tissue - T41A/S45F predicts recurrence risk
• APC germline testing if intra-abdominal/mesenteric location (FAP association)

Workup - Local Imaging

MRI primary site - first-line; T1/T2 characteristics; infiltrative margins

Workup - Biopsy

• Core needle biopsy - confirm before treatment; avoid surgery without biopsy
• IHC: nuclear beta-catenin+ (CTNNB1 mutation)
• CTNNB1 mutational analysis (Sanger sequencing) - T41A/S45F carry Higher recurrence risk
• Exclude sarcoma and fibrosarcoma with IHC panel

Workup - Staging

CT abdomen/pelvis for intra-abdominal desmoids - assess bowel/ureter involvement

Workup - Other

• Genetics referral if mesenteric/intra-abdominal location - colonoscopy surveillance for FAP
• MDT at soft tissue sarcoma centre - watch-and-wait is now first-line for asymptomatic stable lesions

Follow-up Summary

• Active surveillance (watch-and-wait): MRI primary site at 3 and 6 months, then 6-monthly for 2 years, then annually
• Post-surgical: MRI at 3 months, 6 months, then 6-monthly to 5 years; annual MRI to 10 years
• Sorafenib/imatinib therapy: imaging response assessment at 3–6 months; toxicity review at each visit
• No systemic metastatic risk - no CT chest surveillance required
• FAP/APC germline mutation: refer to genetics; colonoscopy surveillance mandatory
• CTNNB1 mutation type (T41A, S45F) may guide recurrence risk stratification
• Discharge at 10 years if stable; intra-abdominal desmoids may warrant continued MDT review