Advances in Cancer Prevention
Open Access

Recent survey data from the Behavioural Risk Factor Surveillance System also have confirmed a move away from stool-based screening methods to lower endoscopy. The question, however, remains, has the increase in colonoscopy utilization over the past decade resulted in a substantial reduction in risk of CRC? There is some evidence that increased colonoscopy efforts are making a difference in reducing CRC disease burden [1]. The most recent national trends in CRC incidence are encouraging. From 2002 to 2005, the annual percentage of change in death rates from CRC has decreased in both men and women by 4.3%. There is also evidence that CRC is being diagnosed at an earlier stage [2]. Finally, for those who have normal colonoscopy findings, the rate of subsequent CRC is quite low. This was first demonstrated by using large administrative data sets. Most recently, a well-described population of 1256 average-risk individuals who all had normal screening colonoscopy results at baseline underwent follow-up colonoscopy approximately 5 years later, and no cancers were detected. However, not all the recent evidence of the effectiveness of colonoscopy has been positive [3]. Although the occurrence of cancer after a colonoscopy with normal findings is infrequent, cancer after a colonoscopy detecting polyps seems much more common. In a recent pooled report of 9167 patients with adenomas, cancer was found after a relatively short interval in 58 patients. 10 Using an algorithm to determine possible reasons for these early cancers suggested that many were preventable, likely being missed or the result of an incomplete resection of a previous lesion [4]. Even more disturbing is the suggestion that colonoscopy may be working less effectively on the right side of the colon. One recent study using administrative data from Canada could not detect any benefit of previous colonoscopy in preventing mortality from rightsided CRC [5]. Although some have suggested that this may have been a phenomenon related to the regional performance of colonoscopy outside the United States, there are data to suggest that detection of lesions on the right side may be suboptimal in this country as well [6]. For example, Kahi recently reported results from a U.S. cohort of 715 patients who underwent colonoscopy in the 1980s. Seven cancers were detected during long-term follow-up, and 6 were in the ascending colon or cecum [7]. These recent reports highlighting potential colonoscopy failures are the backdrop for the current report by Leung in this issue of GIE. The article describes the long-term follow-up of patients who were participants in the Polyp Prevention Trial, a large multi-centre trial of the effect of a low-fat, high-fruit and -vegetable diet on the recurrence of colorectal adenomas [8]. This group previously reported cancer occurring after colonoscopy during the active treatment portion of that trial. Thirteen interval cancers were identified over 5810 personyears of observation [9]. The rate of early interval cancer was certainly higher than that observed in the landmark National Polyp Study, but consistent with that of other reports from the Polyp Prevention Study Group and the Department of Veterans Affairs. The importance of the current article is that it reports on the long-term follow-up for cancer in this well-described cohort [10].

Acknowledgement

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Conflict of Interest

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