Initial colorectal cancer screening more important than surveillance

Initial polypectomy for adenoma patients, with or without surveillance colonoscopy, markedly reduces colorectal cancer (CRC) mortality, suggesting that the initial polypectomy accounts for the greatest component in mortality reduction, according to new research. By comparison, surveillance colonoscopy’s effects on mortality are more modest.

An associate attending biostatistician in the Department of Epidemiology and Biostatistics at Memorial Sloan-Kettering Cancer Center in New York City said that the findings support the guidelines that surveillance intervals can be extended to five or more years in the majority of adenoma patients who are at lower risk for subsequent advance adenomas. Such as those with three or more adenomas, adenomas 1cm or larger, a villous histology or high-grade dysplasia at baseline should have surveillance colonoscopy three years following the initial colonoscopy.

In the study presented at the 2007 American College of Gastroenterology meeting, colleagues simulated what would happen to CRC mortality if adenomas were present but not removed at initial or further surveillance exams, if only an initial colonoscopy was performed with polypectomy but no further colonoscopy procedures were done; and finally, if both initial and surveillance colonoscopies were performed. Based on the three models, they assessed the impact of the initial and surveillance colonoscopy.

Because of ethical considerations, such a study could not be done clinically, so the team applied a microsimulation screening analysis (MISCAN) model developed in the Netherlands in conjunction with the National Cancer Institute and used data from the National Polyp Study (NPS) to predict CRC mortality for up to 30 years after initial polypectomy.

The model demonstrated a dramatic reduction in expected CRC mortality with initial polypectomy with or without surveillance and suggested that the initial polypectomy accounts for the major component of mortality reduction. The model predicted a modest benefit from surveillance after 10 years. The authors of the study wrote that “the major effect on CRC mortality reduction produced by the initial polypectomy rather than surveillance colonoscopies is consistent with the low incidence of advance adenomas (1 cm or larger, villous component, high grade dysplasia or invasive CRC) observed during NPS follow-up. This supports the recommendation for lengthening the surveillance intervals to five or more years for most patients’ postpolypectomy.”

The microsimulation modeling was essential because the scenarios could not be done in any clinical practice, since current recommendations call for removal of all polyps when they are discovered.

An associate professor of clinical medicine and director of the Gastrointestinal Health Outcomes, Policy and Economics Research Program at the University of California, San Francisco, and chief of clinical gastroenterology at San Francisco General Hospital pointed out that the findings demonstrate the importance of focusing our efforts on getting anyone screened rather than on repeated surveillance. That’s where the most benefit occurs, and that’s where we should logically apply most of our limited resources. Lengthening colonoscopy surveillance interval would also free up more resources to be applied toward initial screening.

The greater impact of screening compared with surveillance seems to hold true for most types of cancer: The first intervention with a patient is the one that leads to the greatest benefit from both clinical and financial standpoints, while the incremental benefits of periodic surveillance diminish.