Two studies that addressed unrelated, lingering questions about colonoscopy screening should help physicians decide when to recommend the procedure and should help patients decide when to undergo it.
One group of researchers investigated whether it is reasonable to recommend a screening interval of 10 years after a colonoscopy yields negative results. This interval has been widely adopted “based on the estimate of the time it takes for an adenomatous polyp to transform into carcinoma,” but no one has ever demonstrated how long cancer risk remains decreased after a negative colonoscopy.
The second study assessed the value of performing screening colonoscopy in people aged 80 years or older. Current guidelines do not specify when it is reasonable to stop performing the procedure in aging patients, even though the benefits are limited because of their diminishing life expectancies and because the elderly have lower procedural completion rates and higher complication rates than do patients in their 50s or 60s.
In the first study, Dr. Harminder Singh and his associates at the University of Manitoba, Winnipeg, found that the likelihood that colorectal cancer will develop after a screening colonoscopy yields negative results remains low for more than 10 years.
They identified 32,203 members of the general population in Manitoba who had undergone colonoscopy with negative results between 1989 and 2003 and had been followed for at least 6 months for the development of colorectal cancer.
The researchers calculated that the incidence of colorectal cancer (CRC) in these patients was at most 60%–70% of the risk in the general population. “If a patient has a single negative colonoscopy result and does not require further colonoscopy for a particular indication, the likelihood of developing CRC is extremely low, and for this group a screening interval … can be reasonably set at more than 10 years,” Dr. Singh and his associates wrote (JAMA 2006;295:2366–73).
In the second study, Dr. Otto S. Lin of Virginia Mason Medical Center, Seattle, and his associates estimated the mean extension in life expectancy after colonoscopy screening in 1,244 patients who underwent screening between 2002 and 2005. The subjects were categorized by age: 1,034 were aged 50–54 years, 147 were aged 75–79 years, and 63 were aged 80 years or older. The prevalence of neoplasias increased with age. The oldest group had 14% prevalence, compared with 3% in the youngest group.
Nevertheless, screening colonoscopy extended life expectancy only by a mean of about 1 month in the oldest patients, compared with a mean of nearly 1 year in the youngest group. This is because the oldest patients “are much more likely to die of 'natural' causes before an adenoma turns into cancer, thus negating any potential benefits of colonoscopy and polypectomy,” Dr. Lin and his associates wrote (JAMA 2006;295:2357–65).
“Currently, very elderly patients and their physicians are using individual judgment to decide whether to undergo screening. These decisions are based on scant data regarding the impact of screening colonoscopy on life expectancy,” the authors noted.
Physicians and patients should keep in mind not only that the gain in life expectancy may be small but also that procedure times are longer, rates of completed cecal intubation are lower, risks of bowel perforation are higher, and suboptimal bowel preparation is more likely in the elderly, the researchers added.