Editing Soft tissue sarcoma (section)

=== '''Desmoid fibromatosis''' (aka desmoid tumour, fibromatosis, aggressive fibromatosis) ===

** Non-metastatic neoplasm but aggressive locally
** Can be a/w FAP/Gardner syndrome/Turcot syndrome, concurrent with a pregnancy (often stabilises post-partum), or sporadically
** Pathophysiology
*** Clonal proliferations of myofibroblasts - well-differentiated bundles of spindle cells with abundant collagenous matrix
*** Often indolent tumours which show no growth after presentation
*** Sporadic (75-85%):
**** Associated with mutations of CTNNB1 gene -> beta-catenin accumulation and nuclear effects including proliferation
**** Can occur after surgery, trauma, pregnancy, OCP use
**** Those occurring in pregnancy have a good prognosis, and can usually be monitored throughout pregnancy
*** Associated with FAP:
**** 10-15% of patients with FAP will develop a desmoid tumour, mostly within mesentery or abdominal wall, at the site of the scar
**** Caused by germline APC mutations -> beta-catenin accumulation and nuclear effects including proliferation
**** Aggressive, often involving mesentery, occasionally encasing mesenteric vessels
** Workup
*** MRI or CT - homogenous and solid - indistinguishable from other STS subtypes
*** Diagnosis established by core biopsy, if tumour histology will alter treatment
** Management
*** Primary non-operative management, especially for tumours in difficult locations, due to the high risk of local recurrence and possibility of regression (20-30%)
*** Systemic therapies should probably be trialled prior to surgery
**** Nirogacestat - oral gamma secretase inhibitor
**** Tyrosine kinase inhibitors - sorafenib
**** Cytotoxic chemotherapy can be used for locally aggressive or symptomatic tumours
**** It's unclear whether NSAIDs and hormonal therapies are effective
*** Radiotherapy can be used for extremity tumours, or other locations without other good treatment options
*** '''Asymptomatic or mildly symptomatic:'''
**** Initial active surveillance (imaging every 3-6 months)
*** '''Moderately or severely symptomatic:''' 
**** ''Depends on FAP status, location, toxicity of therapy, and desired urgency of response''
**** FAP - usually trial systemic first
**** Sporadic
***** Abdo wall - resection and reconstruction
***** Other location - prefer systemic therapy first
*** '''Imminent threat to life (e.g. bowel obstruction):'''
**** Surgery, if resectable
*** '''Recurrent/relapsed disease:'''
**** Surgical resection +/- adjuvant radiotherapy as salvage
** Prognosis
*** 30% spontaneously regress
*** Sporadic abdo wall desmoids do have a good surgical outcome though