What are desmoid tumors, their etiology, and how are they managed and surveilled?

Desmoid Tumors: Etiology, Management, and Surveillance

Desmoid tumors, also known as desmoid-type fibromatosis, are rare benign but locally aggressive fibroblastic neoplasms that require a watchful waiting approach as initial management in most cases, with active treatment reserved for progressive or symptomatic disease. 1

Definition and Etiology

• Desmoid tumors are monoclonal fibroblastic proliferations characterized by locally invasive behavior with high local recurrence rates but no metastatic potential 2
• These tumors are associated with mutations in either:
  • CTNNB1 gene (β-catenin) in sporadic cases (most common) 3
  • APC gene in cases associated with Familial Adenomatous Polyposis (FAP), representing 5-15% of cases 3
• Both mutations result in abnormal β-catenin accumulation within cells, affecting the Wnt signaling pathway 4
• Risk factors include:
  • Prior trauma or surgery
  • Pregnancy (progression risk during pregnancy is 40-50%)
  • Oral contraceptives
  • Familial history (especially in FAP patients) 1, 5

Classification and Presentation

• Desmoid tumors are classified based on location:
  • Intra-abdominal (often associated with FAP)
  • Abdominal wall (better prognosis)
  • Extra-abdominal (extremities, trunk, head and neck) 5
• Tumor location significantly affects prognosis, with abdominal wall having better outcomes compared to extremities 1
• Biological behavior is highly variable - some tumors spontaneously regress (20-30% of cases), some remain stable, while others grow aggressively 1

Diagnosis

• Histopathological diagnosis is mandatory 3
• Imaging evaluation includes:
  • MRI is the preferred modality for follow-up due to lack of radiation exposure 1
  • CT scan for intra-abdominal lesions
  • Ultrasound may be used for initial assessment 5
• Molecular testing for CTNNB1 or APC mutations can be helpful when pathological diagnosis is difficult 2

Management

Initial Approach

• Watchful waiting is now recommended as the initial approach for most asymptomatic patients, replacing immediate surgery as the standard first-line treatment 1
• This approach has shown progression-free survival rates of 50% at 5 years 1
• Close observation is essential, with regular follow-up to detect progression 1

Surgical Management

• Surgery is indicated when:
  • Watchful waiting fails (disease progression)
  • Complications occur (bowel obstruction, perforation)
  • Major cosmetic issues are present 1
• For FAP-associated intra-abdominal desmoids, surgery should be restricted to treating secondary effects of the disease and performed only in expert centers 1
• When surgery is performed, the goal should be obtaining negative microscopic margins while preserving function 1
• Surgical margins do not consistently correlate with recurrence rates, while β-catenin mutational status does 1

Non-surgical Treatments

• For FAP patients with intra-abdominal or abdominal wall desmoids, sulindac in combination with high-dose selective estrogen receptor modulators may be effective 1
• In case of progression where surgery would cause significant functional loss, consider:
  • Medical treatment
  • Radiotherapy 1

Surveillance

• For asymptomatic patients under watchful waiting:
  • Regular clinical assessment
  • MRI surveillance to assess response to treatment (decrease in T2W signal and lesion size) 1
  • Serial imaging with CT or MRI every 6-12 months depending on growth rate 1
• For FAP patients:
  • Consider determining genotypes or family history of desmoid disease before colectomy, as these may predict desmoid formation 1
  • Radiological screening at 12 months following diagnosis is suggested 1

Special Considerations

• Pregnancy is not a contraindication for women with desmoid tumors, as most cases can be safely managed despite a 40-50% progression risk during pregnancy 1
• Pain alone should not be considered an unequivocal indication for surgery 1
• Patients with desmoids in critical locations (mesentery, head and neck) may require more aggressive management due to potential life-threatening complications 2