A new study shows that colonoscopy actually prevents cancer deaths. Although many people have assumed that colonoscopy must save lives because it is so often recommended, strong evidence has been lacking until now.
Colorectal tumors are a major cause of cancer death in the United States and one of the few cancers that that can be prevented with screening. This year, more than 143,000 new cases and 51,000 deaths are expected. Incidence and death rates have been declining for about 20 years, probably because of increased use of screening tests and better treatments. But only about 6 in 10 adults are up to date on getting screened for colorectal cancer, according to federal estimates.
For the study the patients were tracked for as long as 20 years, the death rate from colorectal cancer was cut by 53 percent in those who had the test and whose doctors removed precancerous growths, known as adenomatous polyps, researchers reported on Wednesday in The New England Journal of Medicine. The test examines the inside of the intestine with a camera-tipped tube.
A team of researchers led by Dr. Sidney J. Winawer, a gastroenterologist at Memorial Sloan-Kettering Cancer Center in New York City, followed 2,602 patients who had adenomatous polyps removed during colonoscopies from 1980 to 1990. Doctors compared their death rate from colorectal cancer with that of the general population, where 25.4 deaths from the disease would have been expected in a group the same size. But among the polyp group, there were only 12 deaths from colorectal cancer, which translates into a 53 percent reduction in the death rate. The new study did not compare colonoscopy with other ways of screening for colorectal cancer and so does not fully resolve a longstanding medical debate about which method is best. Tests other than colonoscopy look for blood in the stool or use different techniques to examine the intestine.
“For any cancer screening test, reduction of cancer-related mortality is the holy grail,” said Dr. Gina Vaccaro, a gastrointestinal oncologist at the Knight Cancer Institute at Oregon Health and Science University who was not involved in the research. “This study does show that mortality is reduced if polyps are removed, and 53 percent is a very robust reduction.”
Earlier research had proved that removing precancerous polyps could greatly reduce the incidence of colorectal cancer. However if removal of polyps actually saved lives was a question. “This study puts that argument to rest,” said Dr. David A. Rothenberger, a professor and deputy chairman of surgery at the University of Minnesota Masonic Cancer Center. He was not part of the study. Robert A. Smith, the senior director for cancer control at the American Cancer Society, said, “This is a very big deal.”
“Not all adenomas become cancers, and not all cancers cause death,” said Ann Zauber, the lead author of the study and a statistician at Sloan-Kettering. But in many cases, she said, “we have gotten those that would have had the potential to go on and cause a cancer death.”
But Dr. Harold C. Sox, an emeritus professor of medicine at Dartmouth Medical School and former editor of a leading medical journal, Annals of Internal Medicine, cautioned that the new study was not the last word. He said it was not clear that the same reduction in the death rate found in the study would occur in the general population. Nonetheless, he said, “I suspect that removing polyps does reduce colorectal cancer mortality.”
Dr. Sox also said that because all of the patients in the study had adenomatous polyps, it is not certain that the findings would apply exactly to the general population, in which this type of polyp is found in about 15 percent of women and 25 percent of men. In addition, Dr. Sox said, the people with polyps were part of a study that provided high-quality colonoscopy, so they may not have been comparable to the general population.
Durado Brooks, director of the American Cancer Society’s prostate and colorectal cancer division, says the findings are in line with smaller studies suggesting that polyp removal and surveillance can cut colorectal deaths in half. “This research provides solid data to confirm this,” he tells WebMD. “But it is not all good news. Even though the death rate was reduced by half, people in this group still died of colorectal cancer.”
Twelve of the patients died of the cancer an average of about a decade (the range was six to 22 years) after having polyps removed during colonoscopy. Five of these fatal cancers were diagnosed during follow-up surveillance. “Colonoscopy is an extraordinary tool, but it is not infallible,” Brooks says. “Once a polyp is found, people need to be rechecked on a regular basis.”
Colonoscopy does not have to be done every year: If there are no polyps, it is recommended just once every 10 years. People with polyps are usually told to have the test every three years. But colonoscopy is expensive, costing hundreds or thousands of dollars, depending on whether polyps are removed and on the part of the country where it is done. It also carries small risks of bleeding or perforation of the intestine. And it requires sedation as well as strong laxatives to clean out the intestines so that the doctor can look for polyps.
“Any screening is better than none,” Dr. Winawer said. “The best test is the one that gets done, and that gets done well.” His study was paid for by the National Cancer Institute, Memorial Sloan-Kettering Cancer Center and private foundations dedicated to colon cancer.
The American Cancer Society recommends that men and women get a colonoscopy or another colon cancer screening test such as fecal occult blood test starting at age 50, according to its website. Colonoscopy should be done every ten years, it recommends.
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