The malignant potential of freshly developed colorectal polyps according to age.

BACKGROUND Although malignant colorectal neoplasms are found more frequently in older population, polyps found at one-time colonoscopy may be a mixture of lesions that developed at various earlier ages. Newly developed adenomas found at the follow-up colonoscopies will reflect the exact relation between malignant potential and the age of development of colorectal polyps. METHODS The results of 44,065 follow-up colonoscopies on 11,912 subjects were analyzed. The proportion of invasive cancer or high-grade dysplasia among all neoplasms, "proportion of malignancy," was evaluated in relation to age groups (young: <50 years old; middle: 50-59 years old; and old: >or=60 years old). RESULTS At the follow-up colonoscopies, a total of 8,271 newly developed neoplasms were found, of which 41 (0.50%) lesions were malignant. The proportion of malignancy was 0.35%, 0.31%, and 1.07% in the young, middle, and old age groups, respectively (P(trend) = 0.002). This trend remained significant when stratified by the size of polyps. The proportion of malignancy was higher on the left-side colon than on the right-side colon, except in the old age group, where it was similar on either side. The proportion of malignancy at the follow-ups was not associated with the lesions found at the initial colonoscopies. CONCLUSIONS The development of malignant lesions in small sizes increased on the colon or rectum at older ages.