Of 1,297 patients, mean age 65.3 years at PPT-CFS study entry, who had colorectal adenomas removed and underwent a mean of 3.3 colonoscopies over a median of 4.3 years of follow-up during the PPT, and who were then followed for an additional mean of 6.2 years during the PPT-CFS, nine cases of colorectal cancer were diagnosed for an incidence rate of 1.2 per 1,000 person-years of observation. Of the new colorectal cancer cases diagnosed during the PPT-CFS, 78 percent of patients had a history of an advanced adenoma, compared to only 43 percent of patients who remained cancer free. Eight out of the nine cancers were located in the proximal colon, where studies have suggested that colonoscopy is less successful in detection. In addition, researchers found that 78 percent of the new colorectal cancer cases diagnosed during the PPT-CFS were diagnosed in men and 44 percent had a family history of colorectal cancer. At diagnosis, the majority of the cancers, 78 percent, were stage I or stage II, a point at which they are highly curable.

Previously, multiple explanations for interval cancers have been proposed. In this study, four of the cancers were detected in colon segments where a polyp was previously found, two were determined to be attributed to incomplete removal of a previous adenoma and biopsy detection of a neoplastic lesion failed in the other two cases. Of the five cases that were detected at previously polyp-free segments, one case was missed, two were newly developed cancers and two cases were owing to indeterminate reasons.

Researchers noted some study limitations, including only a small number of cases of colorectal cancer were identified limiting statistical analysis and 68 percent of those originally enrolled in the PPT participated in the PPT-CFS, which could have led to a biased sample. They concluded that despite frequent colonoscopy during the PPT, there was a persistent ongoing risk of cancer in the years after the trial. Patients with a history of advanced adenoma are at increased risk of subsequent cancer and should be followed closely with continued surveillancelorectal Cancer Screening Guidelines

Guidelines regarding colorectal cancer screening are available at www.asge. Visit ASGE's colorectal cancer awareness Web site at www.screen4coloncancer for more information and to find a qualified physician in your area.At-Risk Populations

One important finding of this study is that patients with a history of advanced adenomas had a higher ongoing risk for subsequent cancer, even above that of subjects with non-advanced adenomas. Follow-up exams for patients with advanced adenomatous polyps are very important, even after a negative follow-up colonoscopy, since the data suggest that the risk of cancer persists. Quality Colonoscopy Screening

This study also highlights the importance of quality colonoscopy screening, since some of the interval cancers appeared to be missed or to have developed at sites where a previous adenoma had been detected. ASGE, as the standard-setting society for endoscopy, has issued quality indicators for colorectal cancer screening that define measures for improving quality in colonoscopy. Experts in gastrointestinal endoscopy should encourage their patients to take their bowel prep as directed before the colonoscopy. Proper bowel prep is important so that the physician can clearly see the colon. In addition, endocopists must be mindful of the importance of not withdrawing too soon during the procedure, allowing enough time to thoroughly examine the colon. According to ASGE quality indicators, average withdrawal time should be six minutes or more.

Source: American Society for Gastrointestinal Endoscopy