Sigmoidoscopy May Miss Cancer

Friday, July 21st 2000, 12:00 am

By: News On 6

Sigmoidoscopy, the most widely used fiber-optic screening exam for colon cancer, is likely to miss diseased growths as much as one-third of the time, researchers say in a study that could lead to wider use of a more thorough method, colonoscopy.

The findings, along with a second study reported in Thursday's New England Journal of Medicine, deepen doubts about the reliability of sigmoidoscopy.

Both sigmoidoscopy and colonoscopy use a flexible tube that is inserted in the rectum to examine the large intestine for cancerous or precancerous polyps.

Sigmoidoscopy, which reaches only part way up the colon, is commonly used for checking patients at no special risk for colon and rectal cancer. Colonoscopy, which reaches all the way up the colon, is widely used for higher-risk patients, such as those with a family history of the disease, blood in stool, or previous growths in their colon.

``These two articles are changing the ground rules a bit,'' said Dr. Harris Clearfield, a professor of medicine at MCP Hahnemann University in Philadelphia. ``There will definitely be lives saved with colonoscopy in average-risk patients, and I think there's going to be increasing attention paid to it.''

Colon and rectal cancer killed about 56,000 people in the United States last year. Colorectal cancer is second only to lung cancer in causing cancer deaths. About 130,000 cases were diagnosed last year.

Sigmoidoscopies are carried out in a doctor's office without sedation and generally cost less than $200. Colonoscopies require sedation and normally take place in hospitals or special surgical sites at a cost of $700 or more. Tearing and other serious bleeding, though rare, happen more often with colonoscopies.

In sigmoidoscopy, the tube is inserted only about two feet up the colon. The device shows the colon on a video screen and removes any worrisome growths. If such growths are found, a colonoscopy will usually be performed later to examine the entire colon, which snakes up about five feet to the small intestine.

In the largest study ever of colonoscopy, researchers examined 3,121 men ages 50 to 75 with no symptoms of colon or rectal cancer at 13 U.S. veterans hospitals. At least 52 percent with cancer or advanced precancerous polyps in the upper colon had no precancerous polyps in the lower colon or rectum. Altogether, between 20 percent to 32 percent of men with advanced growths would thus be overlooked by sigmoidoscopy alone.

``If I'm a patient and I'm going to be told there's a 1-in-3 or a 1-in-5 chance we're going to miss something on that exam, I'm not sure I'd be reassured,'' said Dr. David Lieberman, the lead researcher at the Veterans Affairs Medical Center in Portland, Ore.

The second study, carried out at Indiana University Medical Center and three other sites, analyzed colonoscopy results from screenings of 1994 men and women in a health program at Eli Lilly and Co., the drug maker. Sixty-two percent with advanced polyps in their upper colon showed no precancerous polyps in the lower section.

In an accompanying editorial, Dr. Daniel Podolsky of Massachusetts General Hospital in Boston said colonoscopy could, at least in theory, eradicate the vast majority of colorectal cancer.

Relying on sigmoidoscopy makes as much medical sense as ``performing mammography of one breast to screen women for breast cancer,'' he said.

Most government and private health organizations recommend that people 50 and older be screened for colon and rectal cancer with sigmoidoscopy every five years and each year with a test that detects blood in the stool. Insurance companies generally cover those two tests to screen healthy patients.

Dr. Thomas Imperiale, who led the second study, said he favors broader use of colonoscopy for older patients or others who may be at higher risk. But he added, ``To go to a strategy of screening everyone with colonoscopy doesn't make sense.''

``It is invasive, it is costly, and we're talking about millions of people,'' said Dr. Sidney Winawer of Memorial Sloan-Kettering Cancer Center in New York. While also advocating more colonoscopy, he said other research must clarify the role of colonoscopy in preventing deaths.

About three quarters of patients with insurance coverage fail to seek colon cancer screening already. ``If you go to colonoscopy, there may be more resistance,'' warned Dr. Donald Young, medical director of the Health Insurance Association of America.