HOUSTONColorectal cancer mortality has declined slightly in the
last 10 years, and the decrease appears to be accelerating. This
decline is due in large part to screening and early detection, said
Patrick M. Lynch, MD, associate professor of medicine, University of
Texas M.D. Anderson Cancer Center.
Dr. Lynch addressed current colorectal screening recommendations and
controversies at a week-long medical oncology review sponsored by
M.D. Anderson Cancer Center.
the general population, the lifetime risk of developing colorectal
cancer is 5%. The percentages rise to 15% to 20% for individuals with
a personal history of colorectal cancer or adenomas, 15% to 40% for
those with inflammatory bowel disease, 70% to 80% in families with
hereditary nonpolyposis colorectal cancer (HNPCC), and more than 95%
for those with familial adenomatous polyposis (FAP).
Screening recommendations are based on assignment of patients into
average-risk, moderate-risk, and high-risk groups (see Table), Dr.
Dilemmas in Average-Risk Persons
Average-risk individuals continue to pose surveillance dilemmas, and
the optimal protocol remains to be determined. Among average-risk
patients, age is probably the single most important factor that
determines the need for screening.
In this group, age 50 remains the magic number, Dr. Lynch
said, only because that is where the risk for colorectal cancer
really takes off. He noted, however, that the disease does seem
to be occurring more often in younger patients.
Fecal occult blood testing (FOBT) remains a mainstay of average-risk
screening despite limitations in sensitivity and specificity.
False-positive tests are common and are often attributable to other
sources of colorectal bleeding or to dietary interference, such as
peroxidase activity in red meats, vegetables, and some fish.
False-negative tests can be caused by such things as ingestion of
vitamin C or a delay in sample processing.
Moreover, Dr. Lynch said, FOBTs low cost must be weighed
against the cost of performing follow-up tests, typically
colonoscopy, after a positive result. Studies suggest that
colonoscopy after a positive FOBT has a cancer-detection rate of
about 10% to 15% and an adenoma detection rate of 40% to 50%.
The degree of mortality reduction associated with FOBT screening
varies widely among the various controlled trials, ranging from 19%
to 57%. Despite the considerable scatter in the
reductions, Dr. Lynch said, we now have hard data that FOBT
Underuse of the test, however, continues to be a concern. A
multistate assessment of colorectal cancer surveillance found that
only one fourth to one third of the people who should be having FOBT
were actually having it done, Dr. Lynch noted. So there
continues to be a disconnect between what we recommend and what
Sigmoidoscopy is associated with even greater mortality
reductions59% in a Kaiser-Permanente study reported in the
early 1990s and similar benefits in more recent trials. The
caveatand the techniques greatest limitationis that
these mortality reductions apply only to lesions within the reach of
Questions to Be Answered
Among the questions that need to be answered are the following: Which
lesions found by sigmoidoscopy predict proximal neoplasia? and Can
mortality reductions be improved by combining sigmoidoscopy with FOBT
or air-contrast barium enema?
If you detect an adenoma on sigmoidoscopy, does the size of the
adenoma, the degree of dysplasia, or the number of adenomas predict
proximal neoplasia? Standard of care is to always perform
co-lonoscopy, Dr. Lynch said.
But, he added, adenomas of less than 1 cm are not strong predictors
of proximal risk and may not warrant colon-oscopy. Hyperplastic
polyps, which were once thought to be a predictor of proximal
neoplasia, have now been shown not to predict proximal risk.
Concerning the question of whether mortality reductions with
sigmoidoscopy could be improved with combined FOBT or air-contrast
barium enema, the answer is yesbut the extent of the mortality
reductions is not known, he said.
Sigmoidoscopy, like FOBT, is underutilized. Less than half of
individuals in the target age range have ever had sigmoidoscopy,
Dr. Lynch said. So, again, we have a mortality reduction test
out there, but people really arent availing themselves of it.
Because of the limitations of current screening methodssuch as
false-negatives with FOBT and the limited reach of
sigmoidoscopycolonoscopy is being looked at as a potential
surveillance method in the general population.
More and more data are starting to be compiled on the use of
whats being called primary colonoscopy to screen average-risk
individuals, Dr. Lynch said. With increasing patient
age, the likelihood of identifying a colorectal neoplasm on
Among individuals undergoing colonoscopy for the first time at age 60
or 65, he said, about 30% of women and about 40% of men will have a
polyp or cancer identified. I think the emphasis more and more
is that it simply isnt enough to be screening for cancer,
he said. We want to detect adenomas so that we can remove them
and actually prevent colorectal cancer.
Dr. Lynch added that as the cost of colonoscopy is coming down,
cost-benefit models suggest that the yield from colonoscopy may be
significantly greater than the difference in cost among the various
surveillance methods. He predicted that primary colonoscopy
increasingly will be recommended more strongly as a screening alternative.
I wouldnt be surprised if in the next 10 to 15 years
colonoscopy comes to be the preferred method of surveillance,
he said, simply because of the greater mortality reductions
that can be achieved with relatively modest increments in cost.
Multiple Choice Proposition
For now, however, Dr. Lynch said, colorectal cancer screening for
average-risk individuals remains a multiple choice proposition, with
recommendations varying by organization.
The American Cancer Society (ACS) currently maintains that
FOBT in conjunction with flexible sigmoidoscopy is preferable to FOBT
alone. As an alternative, ACS recommends total colon
examination: air-contrast barium enema at 5 to 10-year
intervals or colonoscopy at 10-year intervals.
Recommendations from a multidis-ciplinary consensus
development panel convened by the Agency for Healthcare Research and
Quality (AHRQ) (formerly known as the Agency for Health Care Policy
and Research) suggest an annual FOBT and flexible sigmoidoscopy at
Other options offered in the AHRQ-sponsored guidelines, which were
published in the February 1997 issue of Gastroenterology,
include FOBT combined with flexible sigmoidoscopy; air-contrast
barium enema at intervals of 5 to 10 years; or colonoscopy at
intervals of 5 to 10 years.
The US Preventive Services Task Force supports annual FOBT,
flexible sigmoidoscopy (no recommended interval), and combined FOBT
and sigmoidoscopy as screening options. The task force cites
insufficient data, pro or con, to support air-contrast barium enema
or colonoscopy as primary screening tests for average-risk patients.
No One Right Answer
I dont think there is one right answer, Dr. Lynch
said. Right now, all the approaches are considered to be
appropriate for screening the average-risk patient.