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.
