TUESDAY, Oct. 16, 2007 (HealthDay News) -- A first-time colonoscopy to remove precancerous polyps plays a bigger role in reducing the risk of dying from colon cancer than do follow-up screenings done years later, a new study suggests.
Researchers found that patients who forego follow-up colonoscopies in the decade following the initial procedure will still reap the benefits sown by a first removal of polyps -- called a polypectomy.
Post-polypectomy colonoscopies do, however, become more important in protecting against colon cancer death as patients enter their second decade following the first colonoscopy, the study authors said.
"The initial colonoscopy has a major impact -- a huge, huge effect -- on reducing colon cancer deaths," said study lead author Ann G. Zauber, an associate attending biostatistician at Memorial Sloan-Kettering Cancer Center's department of epidemiology and biostatistics, in New York City.
"The risk for dying from colon cancer drops 90 percent after the initial colonoscopy," she said. "And in the first 10 years, 90 percent of that reduction is due to that first procedure. Only 10 percent of the risk drop is due to follow-up colonoscopies."
Zauber presented her findings Monday at the American College of Gastroenterology annual meeting, in Philadelphia.
Her team's conclusions were derived from a review of data on colon cancer incidence and deaths that had been collected by the National Polyp Study. The study had tracked the development of polyps and invasive colorectal cancer following a first-time colonoscopy.
For the new study, Zauber and her colleagues fed the National Polyp Study data into a computer model that projected colon cancer incidence and deaths 30 years down the road. The review included three different types of patients -- those who had no preventive screening of any kind; those who underwent only an initial colonoscopy and polypectomy; and those who had both a colonoscopy/polypectomy and follow-up screenings.
The Sloan-Kettering researchers noted that prior research had indicated that a combination of initial polypectomy and follow-up screenings reduced the incidence of colon cancer by between 76 percent and 90 percent. Previous work had also shown that this dual preventative approach reduced the rate of colorectal cancer deaths by between 69 percent and 92 percent.
However, the new analysis parsed those observations -- revealing that the lion's share of the benefit goes to the initial colonoscopy, not the follow-up surveillance.
The new findings also suggest that too much reliance on follow-up screenings -- which can strain health-care resources while exposing patients to the usual risks associated with any invasive procedure -- may be unjustified, the researchers said.
Still, Zauber said that follow-up colonoscopies aren't without some long-term merit. Over time, the relative importance of such surveillance rises, she noted -- ultimately accounting for approximately 45 percent of colon cancer risk reduction in the second decade following a first colonoscopy.
Zauber stressed that the new findings should not alter current American College of Gastroenterology recommendations about shorter-term surveillance: Namely, that high-risk patients -- such as those with a previous history of colon cancer or polyps -- should undergo follow-up colonoscopies every three to five years.
"The guidelines are quite good for higher-risk patients," Zauber said. "And I would not want to discourage people from surveillance. Lower-risk patients, however, could perhaps wait till the later part of that follow-up period before coming back for another colonoscopy."
Dr. Joseph Martz, chief of the division of colorectal surgery at Beth Israel Medical Center in New York City, also placed a premium on follow-up care.
"Surveillance is very important because 3 and 4 percent of polyps greater than 1 centimeter in size could be missed on a first colonoscopy," he noted. "Hidden behind a fold, hidden elsewhere. And if you miss a polyp the first time it has the potential to develop into cancer over three years, over five years. So, you can't minimize the importance of continued surveillance, even if this study shows that the benefit may be equivocal in the first 10 years."
Two other colon cancer studies -- both focused on elderly screening -- were presented Monday at the gastroenterology meeting.
Researchers with the University of Buffalo and the VA Western New York found that colonoscopies uncover polyps more frequently among patients over the age of 80 than among younger patients. They concluded that age alone should not be the sole deciding factor as to whether an elderly patient should undergo the procedure.
And a team at Scripps Clinic in La Jolla, Calif., found that colonoscopy seems to increase survival rates among the elderly by detecting polyps in patients as old as 84 who are without symptoms despite the onset of colorectal cancer.
More information
To learn more about screening for colorectal cancer, visit the American College of Gastroenterology.
