A 62-year-old woman presents to her physician for routine annual examination. She has no known family history of colon disease and is asymptomatic. Stool cards and flexible sigmoidoscopy were recommended and on flexible sigmoidoscopy a 2.4-cm polyp was noted at 35 cm. A colonoscopy was performed and additional polyps were identified in the descending colon and cecum (Figure 65-1).
Colon polyps seen on colonoscopy. (Reproduced with permission from Michael Harper, MD.)
Colon polyps are growths that arise from the epithelial cells lining the colon.
More than 30% of middle-aged and elderly patients are found to have adenomatous polyps on screening and based on autopsy surveys; fewer than 1% will become malignant.1 The lifetime risk of colon cancer is 4.4%.2
In the first round of screening in the Bowel Cancer Screening Programme in England, of over 1 million subjects aged 60–69 years, 2.5% of men and 1.5% of women had an abnormal test. About 40% underwent subsequent colonoscopy revealing higher risk adenomas (n = 6543) and cancer (n = 1772) in 43% and 11.6% of men and 29% and 7.8% of women investigated.3
Patients with an adenomatous polyp have a 30% to 50% risk for developing another adenoma and are at higher risk for colon cancer.1 This risk is greatest in the first 4 years after diagnosis of the first polyp, and greater if a villous adenoma or more than 3 polyps were found.
Familial adenomatous polyposis of the colon is a rare autosomal dominant disorder associated with a deletion in the long arm of chromosome 5. Thousands of adenomatous polyps appear in the large colon, generally by age 25 years, and colorectal cancer develops in almost all these patients by age 40 years.1 Other hereditary polyposis syndromes include Gardner syndrome, Turcot syndrome, Peutz-Jeghers syndrome, and MYH-associated polyposis, familial juvenile polyposis.1
ETIOLOGY AND PATHOPHYSIOLOGY