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Sporadic Adenomas of the Large Intestine

  • S.B. Ho
  • J.H. Bond

Abstract

Sporadic adenomas of the colon are extremely common in the general western population. The risk increases with age and is higher in men than women. The etiology of sporadic polyps is related to the individual’s genetic background and exposure to environmental agents. Environmental factors that increase the risk of adenoma development include increased levels of dietary fat and decreased levels of specific vitamins and physical activity. Genetic events in colonic epithelium that set the stage for adenoma development include the early events of APC and k-ras gene mutations. The development of advanced adenomas results from accumulated genetic damage in cells within dysplastic or aberrant crypts. This primarily occurs in the setting of chromosomal instability, characterized by aneuploidy and alterations of SMAD2, SMAD4, DCC, and P53 genes. A minority of sporadic adenomas develop as a result of inactivated DNA mismatch repair genes, and are characterized by normal (diploid) DNA content, microsatellite instability, and frequent mutations of TGFβRII. Sporadic adenomas are largely asymptomatic, but may occasionally present with rectal bleeding, anemia, or obstructive symptoms. Diagnosis and treatment of adenomas is primarily by colonoscopy. Screening for the presence of adenomas is accomplished by fecal occult blood testing and/or flexible sigmoidoscopies or colonoscopies. Once adenomas are removed current practice guidelines call for repeat surveillance colonoscopies at 3—5 year intervals. Calcium supplementation can reduce adenoma formation in patients with a previously resected adenoma, but the effect is modest. Primary prevention of colonic adenomas is best accomplished by diets low in fat and high in fiber, fruits, and vegetables; increased physical exercise; and avoidance of smoking, excessive alcohol, and obesity. Primary prevention by dietary supplements of vitamin E, vitamin C, selenium, or calcium; or the use of cyclooxygenase inhibitors (aspirin, sulindac) or selective cyclooxygenase (COX-2) inhibitors is currently under investigation and cannot be recommended for general use.

Keywords

Adenomatous Polyposis Coli Fecal Occult Blood Testing Colorectal Adenoma Flexible Sigmoidoscopy Colorectal Polyp 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer-Verlag Berlin Heidelberg 2004

Authors and Affiliations

  • S.B. Ho
    • 1
  • J.H. Bond
    • 2
  1. 1.GI Section (111D)VA Medical CenterMinneapolisUSA
  2. 2.VA Medical CenterUniversity of MinnesotaMinneapolisUSA

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