Five-Year Risk of Colorectal Neoplasia after Negative Colonoscopy

To the Editor: The rate of 1.3% for advanced adenoma detected approximately 5 years after a negative colonoscopy, is indeed low, as Imperiale et al. report (Sept. 18 issue).1 The rate for detection of any adenoma was 16.0%. What is striking is the low proportion of patients with advanced adenoma relative to the proportion of patients with any adenoma (8.1%). Numerous factors may have contributed to this low observed rate, including a low risk of this condition in the study population, low rates of detection by endoscopists, and low rates observed by pathologists. In the Study of Colonoscopy Utilization, an ancillary to the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial, data from nine U.S. centers were tracked for 589 subjects with nonadenomatous findings on initial colonoscopy (494 subjects with hyperplastic polyps and 95 with no polyps), with repeat colonoscopy within 6 years.2 The rate of advanced adenoma was 4.4%, and the rate of any adenoma 20.5%. The risk of advanced adenoma was thus more than three times as high as that reported by Imperiale et al. Although there are limited followup data available for subjects with negative findings on the initial colonoscopy, the proportion of patients with advanced adenoma relative to the proportion with any adenoma in our study (21.5%) is more consistent with that seen in most colonoscopy cohorts.3-5 Robert E. Schoen, M.D., M.P.H.