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."
Two other colon cancer studies -- both focused on elderly screening -- were presented Monday at the gastroenterology meeting.
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