summary Extra-abdominal Desmoid Tumors are benign, locally aggressive, fibrogenic lesions that are associated with familial adenomatous polyposis (FAP). The condition usually presents in patients between the ages of 25 and 35 with a firm, enlarging soft tissue mass Diagnosis is made with a biopsy showing well-differentiated fibroblasts with uniform spindle cells with elongated nuclei and occasional mitoses. Immunohistochemistry will show a positive stain for estrogen receptor-beta. Treatment may be medical management with tamoxifen or wide surgical excision with radiotherapy depending on the size, grade and location of the lesion. Epidemiology Incidence 900 cases a year in US Demographics younger individuals (25-35 years of age) female>male (3:1) higher incidence in familial adenomatous polyposis (FAP) and Gardner syndrome 4-30% cortical desmoid lesions affect active adolescents Anatomic location most common shoulder (20%) > chest wall/back (17%) > thigh (13%) >50% are extra-abdominal may have multiple lesions in the same extremity subsequent mass usually appears more proximally in the same limb appears in sites of previous surgery or scars cortical desmoid lesions result from chronic tendon traction injury most common location involves posteromedial femur at medial head of gastrocnemius or adductor magnus insertion site Etiology Genetics patient's with familial adenomatous polyposis (FAP) have increased risk for development of desmoid tumors 15% of tumors have adenomatous polyposis coli (APC) gene mutation (gene controls beta catenin) elevated levels of beta catenin in all tumors trisomy in chromosome 8 or 20 Associated conditions Dupuytren contractures Ledderhose disease familial adenomatous polyposis (FAP) Gardner syndrome Symptoms Presentation usually an enlarging mass nerve compression numbness, tingling, motor weakness, stabbing pain Physical exam has a distinctive "rock hard" feel on palpation because tumor is fixed to surrounding tissues poorly circumscribed may be painful and limit motion around joint Imaging Radiographs play minimal role in diagnosis some tumors encroach on/erode bone or trigger periosteal reaction that extends into tumor as "frond like" spicules of bone MRI Indications best means to diagnose exclude multicentric lesions (in the same extremity) findings low signal intensity on T1-weighted images low to medium intensity on T2-weighted images Gadolinium enhances appearance infiltrates muscle 5-10cm in size may erode bone locally Studies Gross specimen gritty white poorly encapsulated Histology Classic characteristics are well-differentiated fibroblasts uniform spindle cells with elongated nuclei and occasional mitoses abundant collagen tumor infiltrates adjacent tissues Molecular Genetics/Immunohistochemisty positive 100% positive for estrogen receptor-beta somatostatin cathepsin D Ki-67 c-Kit negative estrogen receptor-alpha progesterone receptor HER2 Treatment Nonoperative Watch and wait with serial MRI examinations to monitor for progression vast majority of cases, particularly asymptomatic or minimally symptomatic, may be managed initially with a period of monitoring tumors may remain stable and even regress over time cortical desmoid tumors in young adolescents are self-limiting low dose-chemotherapy only / tamoxifen indications inoperable lesions tamoxifen favored for failed/poor candidates for standard chemotherapy works because most lesions occur in women and are more aggressive in women, especially premenopausal tamoxifen works via an estrogen receptor blockage Operative wide surgical resection with radiotherapy indications symptomatic lesion recurrent lesion local recurrence is common (reduced recurrence with radiotherapy) external beam radiation dose 50-60Gy Complications Recurrence margin negative 28% recurrence with surgery alone 6% recurence with surgery + radiation margin positive 39% recurence with surgery alone 25% recurernce with surgery + radiation Prognosis High risk of recurrence Highly unpredictable lesions Occasional spontaneous regression No risk of metastasis or malignant transformation, unless related to radiation