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BACKGROUND

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Desmoid tumors are fibrous mesenchymal neoplasms that arise from deep musculoaponeurotic structures. They may occur sporadically or in association with familial adenomatous polyposis (FAP). Though desmoid tumors lack the ability to metastasize, they are locally invasive, often behaving clinically like low-grade fibrosarcomas. This local tissue destruction can lead to significant morbidity, disfigurement, functional deficit, and death. Desmoid tumors have an unpredictable natural history, with some exhibiting the ability to grow rapidly to large size, while other tumors may remain stable for years, and still others may regress completely without treatment. They have a propensity to recur despite complete surgical resection. Treatment consists of surgery, radiation therapy (RT), and systemic therapies, in varying combinations. The rarity of desmoid tumors, combined with their highly variable clinical course, has made formulating consensus guidelines for treatmentdifficult, and considerable controversy still exists regarding many aspects of management. This chapter will provide an overview of the clinicopathologic features of desmoid tumors and will address the diversity of options available in their treatment.

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EPIDEMIOLOGY

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Desmoid tumors occur only rarely in the general population, with an estimated annual incidence of two to four cases per million individuals.1 In contrast, in patients with FAP, desmoid tumors are much more common, occurring in approximately 10% to 25% of patients.2-4 Studies with higher estimates may reflect the fact that patients with desmoid tumors are often referred to tertiary care centers with expertise in FAP, where many of these studies are performed. Patients with FAP have a risk of developing a desmoid tumor at least 800 times that of the general population.4,5 Of all patients presenting with a desmoid tumor, at least 7.5% will ultimately be diagnosed with FAP.4

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FAP is a cancer predisposition syndrome inherited in an autosomal dominant fashion, caused by a mutation in the adenomatous polyposis coli (APC) tumor suppressor gene. FAP is characterized by the development of hundreds to thousands of adenomatous polyps in the colon and rectum, beginning in adolescence. Without prophylactic colectomy, patients will almost inevitably develop colorectal cancer, usually by the age of 40 years. In addition to colorectal polyps, various extracolonic manifestations are commonly seen in patients with FAP. In 1953, Gardner described patients with a hereditary triad of intestinal polyposis, osteomas, and cutaneous or subcutaneous lesions. This constellation of findings became known as "Gardner syndrome."6 Since that time, it has become clear that almost all families with FAP demonstrate some combination of extracolonic manifestations in addition to polyposis, and these associated extracolonic findings are now grouped under the umbrella of FAP. Various cancers and lesions with malignant potential are more common in patients with FAP, including papillary thyroid carcinoma, hepatoblastoma, brain tumors, pancreatic cancer, adrenal adenomas, duodenal and small bowel adenomas, duodenal cancer, gastric fundic gland polyps, gastric antrum adenomas, and gastric cancer, and desmoid tumors. Additionally, various benign abnormalities are also commonly seen in FAP ...

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