Using a model to predict reductions in death from colorectal cancer, epidemiologists and clinical researchers from Memorial Sloan-Kettering looked at the relative effect of an initial screening colonoscopy which clears pre-cancerous polyps from the colon versus surveillance follow-up colonoscopy. Ann G. Zauber, Ph.D., Sidney J. Winawer, M.D., MACG and colleagues presented their findings at the Annual Scientific Meeting of the American College of Gastroenterology.
"The model demonstrated a dramatic reduction in expected colorectal cancer mortality with initial polypectomy with or without surveillance, and suggests that the initial polypectomy accounts for the major component of the mortality reduction," explained Dr. Zauber.
Using a "MISCAN" model, researchers used National Polyp Study data to predict colorectal cancer mortality among three groups of patients: those with no initial removal of polyps or follow-up surveillance by colonoscopy, compared to patients with only initial polypectomy, and those with both polypectomy and follow-up surveillance. The model predicted mortality of up to thirty years after the initial colorectal exam and removal of pre-cancerous polyps.
According to Dr. Zauber, the major effect on colorectal cancer mortality reduction produced by the initial polypectomy rather than the surveillance colonoscopies is consistent with the low incidence of advanced adenomas observed during National Polyp Study (NPS) follow-up (i.e., pre-cancerous growths in the colon larger than 1 cm, polyps with a villous component, high grade dysplasia or invasive colorectal cancer.)
Dr. Zauber and her colleagues suggest that these findings may support the recommendation to lengthen the interval to six or more years for follow-up surveillance for patients who have polyps removed. Current recommendations by the American College of Gastroenterology call for surveillance colonoscopy in three to five years for follow-up of patients with prior colorectal cancer, prior adenomas or disease with causes increased risk of colorectal cancer.
An editorial by colorectal cancer expert T.R. Levin, M.D, FACG in the August issue of the American Journal of Gastroenterology offers an overview of post-polypectomy surveillance. According to Dr. Levin: "Postpolypectomy and postcancer resection surveillance are among the most common indications for colonoscopy in clinical practice. Together, they account for more than one in five colonoscopies in the Clinical Outcomes Research Initiative (CORI) database. Survey results have also demonstrated that postpolypectomy surveillance for small adenomas and hyperplastic polyps is often recommended by specialists and primary care physicians more frequently than guideline recommendations."* Dr. Levin commented on a study in the same issue of the American Journal of Gastroenterology by Brenner et al. from Germany which Levin believes presents additional evidence to justify extending colonoscopy intervals following polypectomy to five years. According to Levin, performing excessive surveillance colonoscopy is a problem for two reasons. It drains resources better used for initial colorectal cancer screening and diagnosis, and patients are exposed to potential risks associated with each colonoscopy with little benefit.
According to ACG President Dr. David A. Johnson, "there is growing evidence to support the extension of surveillance to longer intervals, all subject to optimal clearing of the colon of precancerous polyps -- which is contingent on adequate resection at the time of polypectomy and adequate visualization of the colon, which depends on adequate bowel preparation, as well as efforts by the endoscopist during the exam. Although given the constraints of a modeling study such as this one from Sloan-Kettering, there need to be prospective trials to support and validate longer colorectal cancer surveillance intervals before changing the current recommendations."
* Levin TR, "Dealing With Uncertainty: Surveillance Colonoscopy After Polypectomy," Am J Gastroenterol 2007;102:1745--1747
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