In late January, the Agency for Health Care Policy and Research (AHCPR) released the first evidence report under its new evidence-based practice initiative. The report indicates that screening has been shown to be effective in detecting early-stage colorectal cancers and their precursors. Early detection and treatment are the primary means of preventing deaths from colorectal cancer.
Colorectal cancer is the third most commonly diagnosed cancer in the United States and the second leading cause of cancer death. It is estimated that in 1996, 133,500 new cases of colorectal cancer were diagnosed, and that colorectal cancer accounted for 54,900 deaths.
"This evidence report will improve the early detection and treatment of colorectal cancer by giving clinicians and others state-of-the-art information on screening and diagnostic tests to help them reduce the mortality from this deadly disease," said AHCPR administrator Clifton R. Gaus. "Our goal is to make this information, and all the evidence reports released in the future, available in the public domain to the widest audience possible."
The evidence-based practice initiative, established in October 1996, will provide medical societies, health-care systems, purchasers, health plans, and others with a scientific foundation for developing and implementing their own clinical practice guidelines, performance measures, and other quality improvement tools. In December 1996, the AHCPR issued a request for proposals to fund evidence-based practice centers to produce future evidence reports and also published a notice in the Federal Register inviting nominations for report topics.
Findings of the Evidence Report
The Colorectal Cancer Screening Evidence Report is based on a systematic review of 3,500 citations from the scientific literature published between 1966 and 1994. The review found evidence that a reduction in deaths from colorectal cancer can be achieved through the detection and treatment of early-stage colorectal cancers and the identification and removal of adenomatous polyps--the precursors of colorectal cancers. Other findings include:
Colorectal cancer incidence rises with age, beginning around age 40, and is higher in men than in women (60.4 vs 40.9 per 100,000 per year).
Survival from colorectal cancer is closely related to the clinical and pathologic stage of the disease at diagnosis. Up to 90% of patients with cancer limited to the bowel wall will be alive 5 years after diagnosis, as compared with 35% to 60% of those with involvement of the lymph nodes, and less than 10% of patients with metastatic disease.
Racial differences in colorectal cancer survival have been observed. The 1983 to 1989 5-year relative survival rate for colon cancer was 61% among white men, 50% among white women, 48% among African-American men, and 49% among African-American women. African-American men and women with colorectal cancer have a 50% greater probability of dying of colon cancer than do white men and women.
Well-established risk factors for colorectal cancer include older age, male sex, history of inflammatory bowel disease, certain hereditary conditions, and a family history of colorectal cancer. However, about 75% of all colorectal cancer occurs in people with no known risk factors.
Most Americans are not screened for colorectal cancer. More than two-thirds of patients present with advanced disease. Information from the National Health Interview Survey (NHIS) indicates that in 1992, only 17.3% of people age 50 and older had undergone fecal occult blood testing in the previous year, and 9.4% had undergone sigmoidoscopy in the previous 3 years.
Screening with fecal occult blood testing has been shown to reduce colorectal cancer mortality. Screening with flexible sigmoidoscopy can reduce colorectal cancer mortality risk, but clinical trials have not been performed that directly assess mortality reduction.
Double-contrast barium enema and colonoscopy are proven methods of identifying polyps and colorectal cancer but have not been studied as screening tests.
Further research is needed to demonstrate the effectiveness of colorectal cancer screening tests and determine optimal intervals for such testing.
New AGA Clinical Practice Guideline
The information contained in the AHCPR's evidence report is the basis for a clinical practice guideline on colorectal cancer screening by the American Gastroenterology Association (AGA) that was published in the February issue of Gastroenterology. The AGA led a consortium that directed an AHCPR-sponsored clinical practice guideline panel on colorectal cancer screening. Work on the AHCPR-sponsored guideline was discontinued when the agency ended its clinical practice guide- line program and began developing evidence reports. The AGA then decided to sponsor its own science based guideline on colorectal cancer screening.
"AGA's use of this information on colorectal cancer screening to develop its guideline on colorectal cancer screening demonstrates the importance and potential impact of AHCPR's Evidence-Based Practice Initiative," noted Dr. Gaus."AHCPR is filling a need for comprehensively reviewed, rigorously analyzed science sought by public- and private-sector organizations to use in improving the quality of health-care services they provide."
An executive summary of the Evidence Report on Colorectal Cancer Screening is available on AHCPR's World Wide Web site (http://www.ahcpr.gov/), from AHCPR's Publications Clearinghouse at (800) 358-9295, and from AHCPR's Instant Fax, (301) 594-2800. The complete evidence report will be available in the near future.