Colorectal Cancer Screening

Summary

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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.

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Background

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 screening.

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 screening.

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.

Methodology

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.

Summary Findings

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 biennial screening.
• 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 screening tests.
• 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 undertaken to:

• 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 life.
• 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 sigmoidoscopy.
• 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 programs.
• 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 syndromes.
• 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