Definition
Fibromatous lesions consisting of clonal proliferations of myofibroblasts
Mostly intraabdominal or abdominal wall, can be on extremities or trunk.
Locally aggressive with a propensity for local recurrence
No known potential for metastasis or dedifferentiation
Often considered low-grade Sarcoma
Histology
Histologically benign (lack nuclear atypia & features of malignancy), however can cause SBO, ureteric obstruction, intestinal ischaemia or perforation, which could be fatal.
Incidence
Rare
< 3% of soft tissue tumours
Age 15-60
Women > Men
Association with FAP
Desmoids affect 15% of FAP pts
Somatic desmoids are usually due to the CTNNB1 gene mutation - which affects beta-catenin protein
Thus, to determine if a desmoid is FAP related or not - test for CTNNB1 gene mutation.
Increased risk if previous abdo surgery, certain positions of the APC mutation, female, pregnancy, FHx of desmoid
Aetiology
Unknown
Somatic mutations in APC gene (5q) have been discovered in the majority of sporadic desmoids
Risk factors:
Previous abdo surgery
Up to 30% of pts previous trauma (incl. surgical trauma)
Female
Pregnancy (? Oestrogen sensitive)
FHx of Desmoid (esp. in FAP)
Classification
Abdominal
Often associated with FAP
Often unresectable due to diffuse infiltration of mesentery
Extra-abdominal
Usually sporadic, effectively treated with local therapy
May be diffuse ‘fibromatosis’ rather than circumscribed mass
Typical sites: abdo wall, shoulder girdle, & buttock region
May be multiple
Clinical Presentation
Most present as slow growing painless mass
Can develop at any site, most commonly
Torso, shoulder girdle and hip/buttock region, and extremities
Location in the muscles or along fascial planes
May be multifocal in a region
Intra-abdo desmoids can be associated with
Intestinal obstruction
Mucosal ischaemia
Functional deterioration in an ileoanal anastomosis
Or abscess / sepsis
Often 2° to fistula to SB
In FAP :
Predilection for surgical sites (e.g. mesentery, abdo wall, site of pouch-anal anastomosis)
Lesions develop within 5yrs after surgery in 50%
Abdominal desmoids tend to occur in women during or following pregnancy
Clinically get a mass that is separate from the uterus
Pathology
? Oestrogens stimulate growth
Non-random chromosomal changes
Esp. Trisomy 8 or 20 - occur in ≥ 1/3 of desmoids
Chromosomal change → Deregulated wound healing
Histology
Desmoids lack pseudoencapsulation
Characterized by small bundles of spindle cells in an abundant fibrous stroma
Fibroblasts concentrate at the periphery of the lesion
Low cellularity, few mitotic figures
No necrosis
Locally infiltrate adjacent structures
Do not metastasize
Investigations
CT is best. MRI may be useful. USS to monitor ureters.
May require biopsy to distinguish from Sarcoma
Management
The first step is a differentiate between sporadic and FAP
In FAP
Prior surgery is a risk factor for the development of desmoids
Intra-abdominal desmoids that develop in patients with FAP are often unresectable because they diffusely infiltrate the mesentery
Recurrences tend to become more frequent and aggressive with each surgical intervention
Multidisciplinary approach that includes systemic therapy is typically required to achieve optimal outcomes for these patientx
Observation
Asymptomatic patients
Consider conservative management
May be best for intra-abdo desmoids
50% will progress by 5 years but 50% will stay stable or regress
Medical treatment
Indications
Symptomatic
Progression on imaging
Asymptomatic in whom progression would cause significant morbidity
Options
Radiotherapy
Radiotherapy (50-60Gy over 6 weeks) → Long-term control in 70-80%
Volume of disease does not appear to affect the probability of local control
Difficult to safely give radiotherapy to retroperitoneum or intra-abdo
Systemic treatment
Surgery
Indications
Sporadic desmoid located in the abdominal wall
Bowel obstruction or impending threat to life
Resection with a wide margin
High local recurrence rates
Prognosis/Natural History
Natural Hx:
10% resolve
30% grow and regress in cycles
50% remain stable
Can be fatal by causing destruction of adjacent vital structures / organs
Fatal in 1-10%
Responsible for death in up to 11% of pts with FAP
Factors associated with poor outcome:
Age 18-30yrs
Presentation with locally recurrent disease
Incomplete excision
Recurrence rates (despite wide margin): up to 80%
Presence of chromosomal changes is associated with a higher risk of recurrence
Subsequent pregnancy is not necessarily a risk factor for recurrence
Follow-up
Clinical exam ± radiology (CT or MRI) long term f/up
6mthly for first 3 years then annually