First colonoscopy has most impact on mortality.

PHILADELPHIA -- The first colonoscopy done on a person has the greatest impact for preventing death from colorectal cancer, and subsequent surveillance colonoscopies play a lesser role, based on a new analysis of 20-year follow-up data collected in the National Polyp Study.

"Initial colonoscopy has a marked and significant impact on reducing colon cancer long term," Ann G. Zauber, Ph.D., said at the annual meeting of the American College of Gastroenterology.

"The current guidelines of colonoscopy surveillance every 3 years for the higher-risk adenoma patients, and less frequent surveillance, every 5-10 years, for the lower-risk adenoma patients, are supported by these findings," Dr. Zauber said in an interview.

"The implication is to use high-quality colonoscopies, and stratify subsequent surveillance to low-risk and high-risk adenoma patients," which is what current guidelines recommend. "This strategy should reduce colorectal cancer mortality and efficiently use colonoscopic resources," said Dr. Zauber, a biostatistician at Memorial Sloan Kettering Cancer Center in New York.

As the analysis by Dr. Zauber and her associates is extended further, it may show that the interval between follow-up surveillance colonoscopies could be lengthened even more for low-risk patients. So far, there is limited evidence on surveillance intervals longer than 5-10 years, she said.

"A goal is to identify low-risk patients in the cohort" who may be able to have less frequent surveillance, commented Dr. Douglas K. Rex, professor of medicine and director of endoscopy at Indiana University in Indianapolis. The type of analysis done by Dr. Zauber may provide useful information that leads to changes in surveillance recommendations, Dr. Rex said in an interview.

Dr. Zauber performed a microsimulation screening analysis on data collected in the National Polyp Study. The study began by screening more than 9,000 people. Out of this group, about 2,600 people were identified with adenomatous polyps, and they were followed over the next 20 years. The National Polyp Study has been led by Dr. Sidney Winawer.

The microsimulation analysis divided the adenoma-carcinoma sequence into stages based on its natural history and generated three models. One model predicted the mortality rate from colorectal cancer if no initial colonoscopy and polypectomy had ever been done, the second model predicted the impact of initial screening only, and the third model calculated the impact of both screening colonoscopy and subsequent surveillance colonoscopies.

If no colonoscopy had ever been done, the predicted 20-year mortality rate from colorectal cancer in patients with adenomatous polyps would be about 5.5%. With screening colonoscopy alone, this mortality rate was cut to about 2.5%. Surveillance colonoscopies lowered the mortality rate still lower, to about 0.9%.

The implication is that the initial screening colonoscopy had the biggest impact on mortality. Surveillance colonoscopies also played a role in further reducing mortality, but the effect was not as great as that of the first colonoscopy.

In earlier reports, researchers from the National Polyp Study showed that patients with three or more adenomas at baseline have an increased risk of subsequent advanced adenomas or colorectal cancer. Current guidelines call for surveillance colonoscopy at 3 years in these patients and in patients with adenomas greater than or equal to 1 cm in size, or with high-grade dysplasia or villous elements. People at lower risk for subsequent advanced adenomas or colorectal cancer can have surveillance colonoscopies at longer intervals. Current guidelines call for follow-up at 5-10 years.

One caveat is that the screening colonoscopies done in the National Polyp Study "did an extremely good job at clearing polyps at baseline," Dr. Rex noted. "We may not see the same impact from screening colonoscopies" in everyday practice, he cautioned, unless the quality of these colonoscopies is very high.

BY MITCHEL L. ZOLER

Philadelphia Bureau