Many doctors recommend a more complete test -- colonoscopy -- but many people refuse that costly, unpleasant exam. The new study shows that the simpler test, flexible sigmoidoscopy, can be a good option. Although it may seem similar to having a mammogram on just one breast, experts say that even a partial bowel exam is better than none.
As one put it, "the best test is the one that gets done."
The study was published online Monday by the New England Journal of Medicine and was to be presented at a digestive diseases conference in San Diego.
Colorectal cancer is the second leading cause of cancer deaths in the United States and the fourth worldwide. More than 143,000 new cases and 52,000 deaths from the disease are expected this year in the U.S. alone.
People ages 50 to 75 who are at average risk of colon cancer are urged to get screened, but only about 60 percent do. Government advisers recommend one of three methods: annual stool blood tests, a sigmoidoscopy (SIG-moy-DAH-skuh-pee) every five years plus stool tests every three years, or a colonoscopy once a decade.
In a colonoscopy, a thin tube with a tiny camera is guided through the large intestine. Growths can be removed and checked for cancer. Patients are sedated, but it requires drinking strong solutions the day before to clean out the bowel.
Sigmoidoscopy is not a popular choice in the United States but it's the one used most often in England. It also uses a thin scope and tiny camera, can be done in an ordinary doctor's office, requires much less bowel preparation and costs just $150 to $300 versus $1,000 to $2,000 for a colonoscopy.
One drawback: It's done without anesthesia. The test usually isn't painful, but patients feel cramping and some discomfort, said Dr. Durado Brooks, the American Cancer Society's colon cancer expert. It also sees only the lower one-third of the colon, "but that is an area where probably half of polyps and cancers develop," Brooks said.
The new study, led by Dr. Robert Schoen of the University of Pittsburgh Medical Center, tested how well it works.
From 1993 to 2001, about 155,000 people ages 55 to 75 were assigned to get the simple scope exam at the start of the study and three to five years later, or usual care -- screening by any means only if they or their doctors wanted it done. Any patients with suspicious findings were sent for a colonoscopy.
After about 12 years of follow-up, there were 21 percent fewer cases of colon cancer and 26 percent fewer deaths from the disease in the group assigned to get sigmoidoscopy.
Of the cancers in that group, 243 were considered to have been caught by sigmoidoscopy (many others were found because of symptoms or other tests). Researchers estimate that 97 more would have been detected if colonoscopy had been the main screening method instead of the simpler scope exam, said study co-leader Dr. Christine Berg, chief of early detection research at the National Cancer Institute, which sponsored the research.
"My opinion is that there's no doubt that colonoscopy would be better in detecting more total cancers," she said. "A sigmoidoscopy could be used in situations where people are afraid of having the bowel prep," or when anesthesia is a risk, she said.
In the study, about half of the group assigned to usual care wound up getting some type of scope exam anyway. That was far more than study leaders expected, and it could have diminished the true benefit sigmoidoscopy gave to the screening group, Dr. John Inadomi of the University of Washington in Seattle wrote in an editorial in the medical journal.
A patient's choice of tests must be respected, he added. "In this case, the best test is the one that gets done."