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Genetics of Colorectal Cancer (PDQ®): Genetics - Health Professional Information [NCI] - Major Genetic Syndromes

Table 5. Extracolonic Tumor Risks in Familial Adenomatous Polyposis continued...

A desmoid risk factor scale has been described in an attempt to identify patients who are likely to develop desmoid tumors.[41] The desmoid risk factor scale was based on gender, presence or absence of extracolonic manifestations, family history of desmoids, and genotype, if available. By utilizing this scale, it was possible to stratify FAP patients into low-, medium-, and high-risk groups for developing desmoid tumors. It was concluded that the desmoid risk factor scale could be used for surgical planning. Validation of the risk factors comprising this scale were recently supported by a large, multiregistry, retrospective study from Europe.[42]

The natural history of desmoids is variable. Some authors have proposed a model for desmoid tumor formation whereby abnormal fibroblast function leads to mesenteric plaque-like desmoid precursor lesions, which in some cases occur prior to surgery and progress to mesenteric fibromatosis after surgical trauma, ultimately giving rise to desmoid tumors.[43] It is estimated that 10% of desmoids resolve, 50% remain stable for prolonged periods, 30% fluctuate, and 10% grow rapidly.[44] Desmoids often occur after surgical or physiological trauma, and both endocrine and genetic factors have been implicated. Approximately 80% of intra-abdominal desmoids in FAP occur after surgical trauma.[45,46]

The desmoids in FAP are often intra-abdominal, may present early, and can lead to intestinal obstruction or infarction and/or obstruction of the ureters.[38] In some series, desmoids are the second most common cause of death after CRC in FAP patients.[47,48] A staging system has been proposed to facilitate the stratification of intra-abdominal desmoids by disease severity.[49] The proposed staging system for intra-abdominal desmoids is as follows: stage I for asymptomatic, nongrowing desmoids; stage II for symptomatic, nongrowing desmoids of 10 cm or less in maximum diameter; stage III for symptomatic desmoids of 11 to 20 cm or for asymptomatic, slow-growing desmoids; and stage IV for desmoids larger than 20 cm, or rapidly growing, or with life-threatening complications.[49]

These data suggest that genetic testing could be of value in the medical management of patients with FAP and/or multiple desmoid tumors. Those with APC genotypes, especially those predisposing to desmoid formation (e.g., at the 3' end of APC codon 1445), appear to be at high risk of developing desmoids following any surgery, including risk-reducing colectomy and surgical surveillance procedures such as laparoscopy.[37,44,50]

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