The importance of screening for colorectal cancer is based on the high incidence and mortality from this cancer and the availability of screening methods of demonstrated efficacy. Cancers of the colon and rectum account for the third largest number of new cancer cases after lung cancer, with 105,500 colon and 42,000 rectum cases estimated, respectively, in 2003; approximately 57,100 deaths were predicted for colon and rectum cancers combined. Whereas declining incidence rates have stabilized since 1995, the steady decline in death rates has accelerated since the mid-1980s, especially for whites.
Four procedures are currently in use for colon cancer screening: fecal occult blood test (FOBT), sigmoidoscopy, colonoscopy, and high-contrast barium enema. All professional organizations that have published guidelines recommend screening for adults 50 years and older with some combination of these four modalities. For the general population, age 50 years was chosen, because that is when the incidence of colorectal cancer begins to increase and where efficacy is supported by evidence. For individuals at high risk, age 40 years is generally recommended as the starting age.
1. Fecal occult blood test, Direct support for use of FOBT comes from three large randomized controlled trials, including a Minnesota trial of 46,501 participants between the ages of 50 and 80 years of age. This study found that annual FOBT with rehydration of the samples decreased 13-year cumulative mortality from colorectal cancer by 33% and biennial screening by 21% Most (75% to 84%) of this reduction resulted from the test itself rather than from incidental discovery of cancers by follow-up colonoscopy. Data from case-control studies are generally consistent with the conclusions of these trials. The main limitation of the FOBT is its limited specificity.
2. Flexible sigmoidoscopy. The advantage of sigmoidoscopy screening over FOBT is that it frequently includes the actual removal of cancer or a precancerous lesion in a biopsied polyp, thus combining screening and treatment in one step. Another advantage is that it needs to be performed only infrequently, perhaps every 5 to 10 years. At least two large randomized trials of flexible sigmoidoscopy screening are in progress. In the first of these randomized trials, the PLCO trial is evaluating the efficacy of examinations every 3 years in 74,000 men and women, 55 to 74 years of age, and an equal number of controls. In the United Kingdom, a trial of 200,000 men and women, 55 to 64 years of age, is evaluating one sigmoidoscopy delivered to approximately 65,000 adults randomized for screening. Meanwhile, supporting evidence for efficacy comes from several case-control studies in health plans in northern California and Wisconsin and from American veterans.
3. Colonoscopy and double-contrast barium enema. No direct evidence supports the efficacy of either colonoscopy or double-contrast barium enema. A strong rationale for the use of colonoscopy is based on its superior sensitivity and specificity. Because there may never be a randomized trial mounted to evaluate the efficacy of colonoscopy directly, choices about its use will depend more on concerns about its safety, the capacity of the health care system to make it available, and its cost effectiveness. Colonoscopy has risks: Approximately 1 in 1000 patients experience perforation, 3 in 1000 have major hemorrhage, and 1 to 3 in 10,000 die as a result of the procedures. Double contrast barium enema is an alternative for examining the entire colon and finds its usefulness in situations in which individuals cannot tolerate endoscopic procedures and in which the relevant expertise exists.
Multiple studies of the cost-effectiveness of colorectal cancer screening are consistent in concluding that the cost per year of life saved is within the limits accepted for most preventive procedures from a societal perspective (approximately $50,000). However, no one modality stands out as superior.
Alternatives to current methods are being investigated and have been reviewed. Immunohistochemical screening tests of stool may offer more sensitive and specific alternatives to guaiac beased testing. The molecular detection of DNA mutations in cells exfoliated from neoplasms in the stool may be a highly sensitive and specific approach that is noninvasive and thus more acceptable to patients.
Newer detection techniques include “virtual” colonoscopy that uses CT of the prepared colon and avoids the invasiveness and discomfort of conventional optical colonoscopy. Fenlon et al provided data on a study in which a crossover design was used; 100 patients were given virtual colonoscopies immediately before conventional colonoscopies. Test performance was compared and was similar, with a threshold of detection for virtual colonoscopy at approximately 5 mm. Pickhardt et al reported on test performance using a similar design but with a much larger population (1233 asymptomatic patients) and one that offers more potential for generalizing findings to average-risk patients. They showed that a three-dimensional endoluminal display can achieve 93.% sensitivity and a specificity of 96.0% for polyps at least 10 mmm in diameter compared to optical colonoscopy on the same asymptomatic average-risk subjects. These and other studies of newer technology will be commanding much attention in the near future.
Meanwhile, despite the evidence supporting the value and cost effectiveness of traditional colorectal cancer screening procedures, compliance with guidelines remains low, at approximately 30% of the population; disparities in screening rates between race and ethnic groups are increasing. Access to screening varies greatly by region of the country and the availability of trained personnel. However, the primary barriers to increased compliance are behavioral for physicians and for patients and associated with the complexity of and perceptions about the nature of the recommended procedures. Efforts to improve compliance should focus on getting individuals over 50 years screened at least once by any modality, rather than on the superiority of any one test. Choices among individuals vary consistently regarding which test is preferred.
Four procedures are currently in use for colon cancer screening: fecal occult blood test (FOBT), sigmoidoscopy, colonoscopy, and high-contrast barium enema. All professional organizations that have published guidelines recommend screening for adults 50 years and older with some combination of these four modalities. For the general population, age 50 years was chosen, because that is when the incidence of colorectal cancer begins to increase and where efficacy is supported by evidence. For individuals at high risk, age 40 years is generally recommended as the starting age.
1. Fecal occult blood test, Direct support for use of FOBT comes from three large randomized controlled trials, including a Minnesota trial of 46,501 participants between the ages of 50 and 80 years of age. This study found that annual FOBT with rehydration of the samples decreased 13-year cumulative mortality from colorectal cancer by 33% and biennial screening by 21% Most (75% to 84%) of this reduction resulted from the test itself rather than from incidental discovery of cancers by follow-up colonoscopy. Data from case-control studies are generally consistent with the conclusions of these trials. The main limitation of the FOBT is its limited specificity.
2. Flexible sigmoidoscopy. The advantage of sigmoidoscopy screening over FOBT is that it frequently includes the actual removal of cancer or a precancerous lesion in a biopsied polyp, thus combining screening and treatment in one step. Another advantage is that it needs to be performed only infrequently, perhaps every 5 to 10 years. At least two large randomized trials of flexible sigmoidoscopy screening are in progress. In the first of these randomized trials, the PLCO trial is evaluating the efficacy of examinations every 3 years in 74,000 men and women, 55 to 74 years of age, and an equal number of controls. In the United Kingdom, a trial of 200,000 men and women, 55 to 64 years of age, is evaluating one sigmoidoscopy delivered to approximately 65,000 adults randomized for screening. Meanwhile, supporting evidence for efficacy comes from several case-control studies in health plans in northern California and Wisconsin and from American veterans.
3. Colonoscopy and double-contrast barium enema. No direct evidence supports the efficacy of either colonoscopy or double-contrast barium enema. A strong rationale for the use of colonoscopy is based on its superior sensitivity and specificity. Because there may never be a randomized trial mounted to evaluate the efficacy of colonoscopy directly, choices about its use will depend more on concerns about its safety, the capacity of the health care system to make it available, and its cost effectiveness. Colonoscopy has risks: Approximately 1 in 1000 patients experience perforation, 3 in 1000 have major hemorrhage, and 1 to 3 in 10,000 die as a result of the procedures. Double contrast barium enema is an alternative for examining the entire colon and finds its usefulness in situations in which individuals cannot tolerate endoscopic procedures and in which the relevant expertise exists.
Multiple studies of the cost-effectiveness of colorectal cancer screening are consistent in concluding that the cost per year of life saved is within the limits accepted for most preventive procedures from a societal perspective (approximately $50,000). However, no one modality stands out as superior.
Alternatives to current methods are being investigated and have been reviewed. Immunohistochemical screening tests of stool may offer more sensitive and specific alternatives to guaiac beased testing. The molecular detection of DNA mutations in cells exfoliated from neoplasms in the stool may be a highly sensitive and specific approach that is noninvasive and thus more acceptable to patients.
Newer detection techniques include “virtual” colonoscopy that uses CT of the prepared colon and avoids the invasiveness and discomfort of conventional optical colonoscopy. Fenlon et al provided data on a study in which a crossover design was used; 100 patients were given virtual colonoscopies immediately before conventional colonoscopies. Test performance was compared and was similar, with a threshold of detection for virtual colonoscopy at approximately 5 mm. Pickhardt et al reported on test performance using a similar design but with a much larger population (1233 asymptomatic patients) and one that offers more potential for generalizing findings to average-risk patients. They showed that a three-dimensional endoluminal display can achieve 93.% sensitivity and a specificity of 96.0% for polyps at least 10 mmm in diameter compared to optical colonoscopy on the same asymptomatic average-risk subjects. These and other studies of newer technology will be commanding much attention in the near future.
Meanwhile, despite the evidence supporting the value and cost effectiveness of traditional colorectal cancer screening procedures, compliance with guidelines remains low, at approximately 30% of the population; disparities in screening rates between race and ethnic groups are increasing. Access to screening varies greatly by region of the country and the availability of trained personnel. However, the primary barriers to increased compliance are behavioral for physicians and for patients and associated with the complexity of and perceptions about the nature of the recommended procedures. Efforts to improve compliance should focus on getting individuals over 50 years screened at least once by any modality, rather than on the superiority of any one test. Choices among individuals vary consistently regarding which test is preferred.
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