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The Malignant Potential of Freshly Developed Colorectal Polyps According to Age

¹ Department of Gastroenterology, University of Tokyo, Tokyo, Japan and ² Department of Gastroenterology, Kameda General Hospital, Chiba, Japan

Requests for reprints: Yutaka Yamaji, Department of Gastroenterology, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan. Phone: 81-3-3815-5411 ext. 33056; Fax: 81-3-3814-0021. E-mail: yamaji-tky{at}umin.ac.jp

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: 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. (Cancer Epidemiol Biomarkers Prev 2006;15(12):2418–21)