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

Table 8. Clinical Practice Guidelines for Diagnosis and Colon Surveillance of Familial Adenomatous Polyposis (FAP) continued...

Level of evidence (celecoxib): 1

One cohort study has demonstrated regression of colonic and rectal adenomas with sulindac (an NSAID) treatment in FAP. The reported outcome of this trial was the number and size of polyps, a surrogate for the clinical outcome of main interest, CRC incidence.[176]

Level of evidence (sulindac): 1

Patients who carry APC germline mutations are at increased risk of other types of malignancies, including thyroid cancer, small bowel cancer, hepatoblastoma, and brain tumors. The risk of these tumors, however, is much lower than that for colon cancer, and the only surveillance recommendation by experts in the field is upper endoscopy of the gastric and duodenal mucosa.[9,22] The severity of duodenal polyposis detected appears to correlate with risk of duodenal adenocarcinoma.[79] (Refer to the Duodenum/small bowel tumors section and the Other tumors section in the Major Genetic Syndromes section of this summary for more information about screening for extracolonic malignancies in patients with FAP.)

Attenuated Familial Adenomatous Polyposis (AFAP)

AFAP is a heterogeneous clinical entity characterized by fewer adenomatous polyps in the colon and rectum than in classic FAP. It was first described clinically in 1990 in a large kindred with a variable number of adenomas. The average number of adenomas in this kindred was 30, though they ranged in number from a few to hundreds.[177] Adenomas in AFAP are believed to form in the mid-twenties to late twenties.[65] Similar to classic FAP, the risk of CRC is higher in individuals with AFAP; the average age at diagnosis, however, is older than classic FAP at 56 years.[27,28,178] Extracolonic manifestations similar to those in classic FAP also occur in AFAP. These manifestations include upper GI polyps (FGPs, duodenal adenomas, and duodenal adenocarcinoma), osteomas, epidermoid cysts, and desmoids.[65]

AFAP is associated with particular subsets of APC mutations, including missense changes. Three groups of site-specific APC mutations causing AFAP have been characterized:[27,28,29,30,179,180]

  • Mutations associated with the 5' end of APC and exon 4 in which patients can manifest 2 to more than 500 adenomas, including the classic FAP phenotype and upper GI polyps.
  • Exon 9-associated phenotypes in which patients may have 1 to 150 adenomas but no upper GI manifestations.
  • 3' region mutations in which patients have very few adenomas (<50).
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