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The Agency for Health Care Policy and Research (AHCPR) is
developing scientific information for other agencies and
organizations on which to base clinical guidelines, performance
measures, and other quality improvement tools, under the Agency's
Evidence-based Practice Initiative, which was launched in the
fall of 1996. At the same time, the Agency ended its clinical practice guideline development program and disbanded its guideline development panels. However, this Technical Review summary of the evidence related to colorectal cancer screening is the work of a clinical practice guideline panel formerly sponsored by AHCPR.
Colorectal cancer is the third most commonly diagnosed cancer
and the second leading cause of cancer death in the United
States. In 1996, an estimated 133,500 new cases of colorectal
cancer were diagnosed, and approximately 54,900 people died of
the disease. In the United States, the incidence of colorectal
cancer is increasing, while the mortality rate is decreasing.
Incidence increases with age, beginning around 40 years of age,
and it is higher in men than in women (60.4 in men versus 40.9 in
women, per 100,000, per year).
Colorectal cancer survival is closely related to the clinical
and pathological stage of the disease at diagnosis. Approximately
65 percent of patients present with advanced disease. Five-year
survival for cancer limited to the bowel wall at the time of
diagnosis approaches 90 percent. Survival at 5 years is 35 to 60
percent when lymph nodes are involved and less than 10 percent
with metastatic disease.
Racial differences in colorectal cancer survival have been
observed. The 1983 to 1989 5-year relative survival for colon
cancer was 61 percent among white men, 59 percent among white
women, 48 percent among black men, and 49 percent among black
women. Analysis of the National Cancer Institute's Black/White
Cancer Survival Study found that black men and women with
colorectal cancer had a 50 percent greater probability of dying
of colon cancer than did white men and women. Colorectal cancer
mortality is low in American Indians and high in Alaska Natives.
Differences in stage of disease at diagnosis, aggressiveness of
therapy, and sociodemographic and cultural characteristics are
factors that have been postulated as contributors to the observed
disparity in survival rates. However, none of these factors
completely explains this observed disparity.
There are many risk factors for colorectal cancer, some of
which are not amenable to change. These include older age, male
sex, inflammatory bowel disease, certain hereditary conditions,
and a family history of colorectal cancer or adenomatous polyps.
Individuals with no predisposing factors are considered to be at
average risk. About 75 percent of all colorectal cancer occurs in
people with no known predisposing factors for the disease.
Preventing Colorectal Cancer Deaths
Evidence exists that reductions in colorectal cancer morbidity
and mortality can be achieved through detection and treatment of
early-stage colorectal cancers and the identification and removal
of adenomatous polyps, the precursors of colorectal cancer.
Colorectal cancer screening tests have been shown to achieve
accurate detection of early stage cancer and its precursors.
Most Americans are not screened for colorectal cancer.
Information from the National Health Interview Survey indicates
that in 1992 only 17.3 percent of people 50 years of age or older
had undergone fecal occult blood testing in the previous year,
and 9.4 percent had undergone sigmoidoscopy in the previous 3
years. To estimate the prevalence of colorectal cancer screening
practices, the Centers for Disease Control and Prevention
analyzed data on use of colorectal cancer screening methods from
the 1992 and 1993 Behavior Risk Factor Surveillance System. Low
rates of use of colorectal cancer screening were documented
nationwide, underscoring the need for efforts to increase
There is a lack of consensus concerning the choice of
screening and surveillance tests, the appropriate screening and
surveillance intervals, and the cost-effectiveness of screening.
AHCPR arranged for the development of an evidence report to
summarize current scientific evidence on colorectal cancer
screening and highlight areas for future research to improve
Reporting the Evidence
Colorectal Cancer Screening, Evidence Report No. 1, is based
on a systematic review of about 3,500 citations from the
scientific literature published between 1966 and 1994.
Select to access the full text of the Colorectal Cancer Screening Technical Review.
The report provides a review of screening for colorectal
cancer and adenomatous polyps in asymptomatic persons at average
risk for colorectal cancer, subsequent diagnostic evaluation in
those with positive screening tests, and surveillance of those
with colorectal disease. Other populations addressed include
persons who have:
- A family history of colorectal cancer.
- A family history of adenomatous polyps.
- Inflammatory bowel disease.
- Familial adenomatous polyposis or hereditary nonpolyposis colorectal cancer.
- Had adenomatous polyps removed.
There are several tests available as options for colorectal
cancer screening, but the evidence supporting their use varies
considerably. The screening tests reviewed for this evidence
report include fecal occult blood testing (FOBT), 60 cm flexible
sigmoidoscopy, FOBT combined with flexible sigmoidoscopy,
double-contrast barium enema (DCBE), and colonoscopy. Evidence
for each screening test is summarized for performance,
effectiveness, possible screening frequency, test complications,
and patient acceptance.
Computer literature searches using Medline from 1966 to 1994
and Cancerlit from 1980 to 1994 were performed. Literature review
was accomplished by (1) establishing a priori criteria for
relevant studies, (2) developing and completing abstract review
forms for each study identified by computer searches and
bibliography scans, (3) compiling and reviewing full articles,
(4) developing and completing a 16-page data collection form for
each article selected for inclusion in the evidence tables, and
(5) compiling evidence tables summarizing these articles.
The significant findings set forth in this evidence report can
be summarized as follows:
- Colorectal cancer mortality can be reduced 15 to 33
percent by FOBT and diagnostic evaluation and treatment
for positive tests. Annual FOBT screening leads to a
greater reduction in colorectal cancer mortality than
- 60 cm flexible sigmoidoscopy identifies nearly all
cancers and polyps greater than 1 cm in diameter and 75
to 80 percent of small polyps that are located in the
portion of the bowel examined.
- Screening with flexible sigmoidoscopy can reduce
colorectal cancer mortality risk. Sigmoidoscopy is
associated with a 59 to 80 percent reduction in risk of
death from cancer in the part of the colon examined by
the rigid sigmoidoscope.
- There is indirect evidence that supports the use of DCBE
in screening for colorectal cancer. DCBE can image the
entire colon and detect cancers and large polyps.
- Screening colonoscopy offers the potential to both
identify and remove cancers and premalignant lesions
throughout the colon and rectum. No studies to date have
been completed that show a mortality reduction associated
with screening colonoscopy.
- There is evidence that detecting and removing polyps
reduces the incidence of colorectal cancer and that
detecting early cancers lowers mortality from colorectal
cancer. Both DCBE and colonoscopy detect polyps and
colorectal cancer, but they have not been studied as
- Evidence suggests a low level of awareness about the
risks of colorectal cancer and its symptoms among adults
in the United States. However, methods to improve
screening compliance have been identified. Patients who
understand the nature of the disease are more likely to
feel that they may be at risk, perceive fewer barriers to
testing, and be more likely to participate in screening.
In addition, good communication between health care
providers and patients and effective use of educational
materials can greatly enhance patient participation and
satisfaction with screening.
Future Research Needs
Necessary evidence does not exist at this time to answer
conclusively many important questions regarding colorectal cancer
screening. To develop this evidence, research should be
- Investigate the optimal screening intervals for currently
available screening test options.
- Translate findings from investigations of the molecular
biology of colorectal cancer pathogenesis into clinically
useful screening interventions.
- Examine the effect of colorectal cancer screening and
subsequent diagnostic evaluation(s) on patient quality of
- Determine the effectiveness of screening flexible
sigmoidoscopy, colonoscopy, and barium enema, ideally
with randomized trials.
- Define more precisely the risk of colorectal cancer for
people with small (less than 1 cm in diameter)
adenomatous polyps as the sole finding identified on
- Characterize more precisely individual risk, according to
such parameters as age, previous screening history,
family history, and genetic background, in order to
inform decisions on how best to tailor screening
- Determine screening effectiveness in patients with
inflammatory bowel disease.
- Determine the prevalence of genetic syndromes and the
benefits of screening in patients found to have genetic
- Define optimal methods to improve patient compliance with
colorectal cancer screening.
- Identify the most effective strategies to raise public
and patient awareness of the magnitude of the risk of
colorectal cancer, its natural history, the importance of
familial risk factors, and the available interventions
for screening, diagnosis, and treatment.
For More Information
Print copies of the Executive Summary (AHCPR Publication No.
97-0302), Evidence Report: Number 1, Colorectal Cancer Screening
(AHCPR Publication No. 97-0300), and the Technical Appendix
(AHCPR Publication No. 97-0301), which contains a complete
bibliography and evidence tables, may be ordered from the AHCPR
Publications Clearinghouse. Call the Clearinghouse at
800-358-9295 (410-381-3150 for callers outside the United States
only; 888-586-6340 for toll-free TDD service for hearing-impaired
callers only) or write to the AHCPR Publications Clearinghouse,
P.O. Box 8547, Silver Spring, MD 20907.
AHCPR Publication No. 97-0302