Doctor's Corner: Screening for colon cancer: Who, why, when and how Doctor's Corner: Screening for colon cancer: Who, why, when and how (June 09, 2004)

By Dr. John Selling

Are you over the age of 50? Are you over the age of 40 with a family history of colon cancer or polyps? Do you have undiagnosed abdominal pain, a change in bowel habits, or blood in your stool?

If you answered yes to any one of these questions, this article is for you.

Colon cancer is the second leading cause of cancer-related death in men and women in the United States. This year, 32,000 men and women will die of colon cancer because they were never adequately screened.

Colon cancer starts as a benign growth, called a polyp, on the inside of the large intestine. On average, it takes about seven to 10 years for a polyp to grow from nothing to becoming a cancer. If it is removed, the whole seven to 10 year process has to start over again. We want to find and remove these polyps before you have symptoms, because after you have symptoms, we may be too late.

What are your screening choices? Fecal occult blood tests show the presence of blood from any source in the stool. Unfortunately, this test is not very sensitive, as the likelihood of a polyp bleeding at the time of the test is low.

Flexible sigmoidoscopy is the same technology as colonoscopy, but views only the lower 40 percent of your colon. Barium enema is an X-ray study of the whole colon, but will miss at least half of the polyps.

Should you choose colonoscopy or virtual colonoscopy? Virtual colonoscopy is a new technology. A computer arranges a series of abdominal X-rays into a sequence to map your large intestine. It requires the same cleaning of your colon prior to the study that colonoscopy does. A tube is inserted into your rectum to inflate the colon with air. The risks are small and discomfort is minimal. No sedation is given.

If a polyp or other abnormality is found, you need to schedule a colonoscopy to have something done about it. Colonoscopy involves the passage of a flexible tube through your entire large intestine (everywhere colon cancer and polyps can be). If any polyp or other abnormality is found during colonoscopy, the doctor can remove it or biopsy it at that time. The risk of puncturing your colon is small (0.03 percent). Sedation is used so you are comfortable.

In the past six months, two studies have been published comparing colonoscopy with virtual colonoscopy. These studies had different results.

One study, published in the New England Journal of Medicine, reported that these two procedures are equal in the finding of colonic abnormalities. This study used a technique and software that is not used anywhere else in the world.

A second study, published in the Journal of the American Medical Association in April, 2004, compared colonoscopy with virtual colonoscopy in nine major hospital centers. In this study, virtual colonoscopy found only 39 percent of small lesions and only 55 percent of larger lesions found by colonoscopy.

Virtual colonoscopy is not good enough yet. Also, if something is found, you have to have a colonoscopy to deal with it.

The three agencies charged with establishing screening guidelines for patients at average risk (Agency for Health Care Policy and Research, American Cancer Society, and American College of Gastroenterology) all recommend colonoscopy every 10 years, starting at age 50. If you have a family history or symptoms, we start at age 40 and may do exams more frequently.

Dr. John Selling is a gastroenterologist at the Menlo Medical Clinic. The Doctor's Corner runs occasionally in the Almanac's monthly Health & Fitness section. If you have a question regarding a particular issue you'd like to see addressed by a Menlo Medical Clinic doctor in a future column, write to the clinic at mmcweb@stanfordmed.org or call 497-8022.

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