than 1 cm will enlarge with time, and within 20 years one third of these become malignant. Thus it is recommended that all polyps that are greater than 0.5 cm should be removed. Furthermore a search for more should be initiated since there is a 30-50% likelihood of finding more polyps, and recurrence is possible, with 77% of recurrent polyps occurring at the site of excision.
Malignancy risk is greater in polyps that are close to a co-existing cancerous growth and/or occur in the distal colon (left side). Villous adenomas (cauliflower-like) are more likely than tubular to become malignant. Persons over 50 have a 30% chance of having adenomatous polyps, but only 3% have polyps larger than 1 cm.
An inherited tendency towards development of hundreds of adenomas is characteristic of several syndromes (hereditary adenomatous polyposis syndromes) (10:244-247). They are transmitted as autosomal dominant traits. Familial adenomatous polyposus coli syndrome virtually always results in colon cancer unless the colon is resected prophylactically. Gardner's syndrome is associated with osteomas, benign, soft-tissue tumors and other extracolonic manifestations such as hypertrophy of the retinal pigment epithelium. All first-degree relatives of patients with these syndromes should be checked for polyps by sigmoidoscopy (see page 16) from age 10-12 up to 35 since the risk of early cancer development is high (94% by age 20, and 98% by 30) (15:84). The responsible mutant gene mutation has been located, and by linkage analysis, affected persons can be identified. But it is not cost effective to screen the general public since they represent only 1% of all colorectal cancer cases.
Another group of inherited syndromes include the so-called "nonpolyposis syndromes" which despite their name, also may derive from adenomas, although many are flat (15:84). They account for 6% of colon cancer cases (10:244). Hereditary site-specific colon c...