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Colon Cancer
  Colonoscopy Versus Sigmoidoscopy

By Francis Pu, PhD

Reviewed by Miriam Komaromy, MD
Last updated February 7, 2011

The relative merits of colonoscopy versus sigmoidoscopy in colon cancer screening has been a source of ongoing debate. The July issue of The New England Journal of Medicine featured two articles and an editorial suggesting that colonoscopy is superior to flexible sigmoidoscopy as a colon cancer screening method. However, experts worry that the articles send the wrong message. That people get regular screening of some sort is more important than what screening tests are used, they say.


What the Studies Found

Half of all ovarian cancers are found in women over the age of 65.
The difference between colonoscopy and sigmoidoscopy is related to which parts of the colon each can examine. Sigmoidoscopy allows doctors to view only the lower part of the colon, while colonoscopy allows doctors to view both the upper and lower sections.

The two studies had similar results:

  • Roughly half of the patients with upper colon abnormalities did not have abnormalities in the lower colon.
  • Between one percent and three percent of patients with no abnormalities in the lower colon had problems in the upper colon.

These studies suggest that colonoscopy is superior to sigmoidoscopy because patients with upper colon abnormalities may slip through the cracks if sigmoidoscopy were the only screening tool. However, doctors do not traditionally use sigmoidoscopy alone, as they did in this study. Instead, sigmoidoscopy is usually combined with a procedure called a fecal occult blood test (FOBT), which detects trace amounts of blood in the stool and can detect cancers forming throughout the colon. For this reason, these studies may not reflect the actual accuracy of the screening that most people receive. "The more valid and relevant comparison is colonoscopy vs. sigmoidoscopy with FOBT," says Miriam Komaromy, Genetic Health's vice president of clinical services.



The Importance of Regular Screening

Colon cancer is one of the most common cancers in American men and women. More than 100,000 new cases are diagnosed each year. The timing of detection is critical. For the one third or so new cases found in the early stages, 90 percent of the patients live at least 5 years after the diagnosis and many live much longer. For the patients with cancer that has reached local lymph nodes and nearby organs, only 65 percent live at least 5 years beyond diagnosis. For patients with cancer that has spread to distant parts of the body such as the liver or lungs, the five-year survival rate drops to below 10 percent. With these odds, it's important that people catch colon cancer in its early stages.

Currently, the American Cancer Society and the American College of Gastroenterology recommend the following screening regimens for people at average risk for colon cancer, beginning at age 50.

  • FOBT every year plus sigmoidoscopy every 5 years


  • Colonoscopy every 10 years



Screening in the Real World

Few gastroenterologists would dispute that colonoscopy is the best test to use for colon cancer screening, according to Jonathon Terdiman, clinical director of the UCSF Colorectal Cancer Prevention Program. However, he also says that FOBT plus sigmoidoscopy is not a bad option, particularly because of how impractical it can be to use colonoscopy as a general screening method. Few specialists are allowed to perform the procedure (in U.S., only about 10,000 specialists for 50 to 70 million patients) and HMOs and other third party payers do not routinely cover colonoscopy. The procedure is also uncomfortable and many people find it embarrassing, which can prevent people from having regular screening. Sigmoidoscopy, on the other hand, is quicker and less expensive than colonoscopy, and is more regularly covered by HMOs. (For recent news about risks associated with colonoscopy, see Related News below.)

Komaromy stresses that the major concern isn't what screening method a person uses, it's that the people who need screening get it. She says that only half of her patients who should be screened actually get regular screening of any kind. In general, only about 30 percent of the population for whom screening is recommended get screened. "We need to focus on encouraging people to get regular screening, regardless of which screening method is the best."

Related News
In order to view these articles you will need to have a MyGeneticHealth account. If you are not already a member, selecting the article will automatically take you to a page where you can sign up.
Colonoscopy perforation risk factors identified
Colonoscopy linked to body salt level disruption




Imperiale, et. al. 2000. Risk of advanced proximal neoplasms in asymptomatic adults according to the distal colorectal findings. NEJM Vol 343, No. 3, pp. 169-174.

Podolsky, Daniel K. 2000. Going the distance : the case for true colorectal cancer screening. NEJM Vol. 343, No.3, pp. 207-208.

Liberman, et. al. 2000. Use of colonoscopy to screen asymptomatic adults for colorectal cancer. NEJM Vol. 343, No. 3, pp. 162-168.

American Cancer Society. 2000. Colon testing can save your life! (Pamplet)

Rex, et. al. 2000. Colorectal cancer prevention 2000: Screening recommendations of the American College of Gastroenterology. The American Journal of Gastroenterology Vol. 95, No. 4, pp. 868-877.

Personal Communication: Miriam Komaromy, MD, Vice President of Clinical Services at Genetic Health

Personal Communication: Jonathon Terdiman, MD, assistant clinical professor of medicine at the University of California, San Francisco and the clinical director of the UCSF Colorectal Cancer Prevention Program



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