Colonoscopy is more effective than less-invasive sigmoidoscopy in preventing colorectal tumors and death, according to a study that supports recommendations for screening every 10 years.
While the study confirms earlier work that showed sigmoidoscopy prevents tumors and deaths from colorectal cancer, it found colonoscopy goes much further. It prevents cancer throughout the colon and cuts the risk of dying from it by 68 percent, according to the study published today in the New England Journal of Medicine.
“This study provides some of the clearest evidence to date that colonoscopy has advantages over sigmoidoscopy for the prevention of colorectal cancer, although it is not a perfect test,” said Andrew Chan, one of the senior authors of the paper and associate professor of medicine at Harvard Medical School.
Both approaches use a flexible tube with a light and a camera attached to examine the lining of the colon. A colonoscopy covers the entire length of the colon, requires preparation to clear out the bowel and generally involves sedation. A sigmoidoscopy covers the lower third of the colon on the left side, involves less bowel preparation and no sedation.
Doctors using either approach can snip off potentially dangerous polyps that are or can become cancerous. Patients who had a negative colonoscopy were less likely to develop colon cancer during the following 15 years, while those who had a polyp removed had a lower risk for just five years, the study found. The American Cancer Society currently recommends that people get screened at age 50 and once a decade thereafter.
A second study of 46,551 patients followed for 30 years confirmed testing blood in fecal matter could detect cancer and reduce deaths. Annual screening using the simple test reduced deaths by 32 percent, while use every other year cut it by 22 percent, according to the follow-up of the Minnesota Colon Cancer Control Study.
The results suggest fecal occult-blood testing remains an acceptable method of screening, the researchers said. After a positive result, patients typically undergo colonoscopy and the removal of any polyps. It’s the removal of those polyps that otherwise may have turned into cancer that most likely provided the survival benefit, the researchers said.
The American Cancer Society estimates 143,000 people in the U.S. will be diagnosed with colon or rectal cancer in 2013, and almost 51,000 will die from the conditions. They are the second most common cause of cancer death, after lung tumors.
The colonoscopy investigation involved 88,902 volunteers from the Nurses’ Health Study and the Health Professionals Follow-up Study and recorded those who underwent a colonoscopy, sigmoidoscopy or neither. They filled out questionnaires every two years between 1988 and 2008. By June 2012, 1,815 developed colorectal cancer and 474 died from it.
If everyone in the study had received a colonoscopy, there would have been 40 percent fewer colon cancers, said lead author Reiko Nishihara, from Dana-Farber Cancer Institute and the Harvard School of Public Health.
The researchers also found that tumors discovered within five years of a colonoscopy were more likely to be a sessile serrated adenoma, a hard-to-detect polyp that may also be fast-growing. Additional efforts to find and remove those polyps are critical, according to Chan, who also works at the Massachusetts General Hospital’s Gastrointestinal Unit.
The sessile serrated polyps have only come to doctors’ attention in the past few years, said James Church, a colorectal surgeon at the Cleveland Clinic, who wasn’t involved with the research. The findings should serve as notice to doctors doing exams to improve the quality, he said in a telephone interview.
“If you’re getting a colonoscopy, you should make sure the person you’re going to is good,” he said. “You always want a good plumber, a good mechanic, a good electrician. But when it comes to a colonoscopy, it could mean your life.”