Invited commentary: Preventing colon cancer: looking over the horizon.

In this issue of BUMC Proceedings, Dr. Stroud reports a multidisciplinary health care improvement initiative that evaluated how well one primary care clinic carried out its objective in screening for colorectal cancer. Improvements in public health and quality of life in the Western world led to dramatic prolongations in life expectancy during the 20th century in association with an alteration in the nature of disease and death. Our concerns have shifted from managing the acute effects of infectious disease (with the periodic eruptions of diseases such as severe acute respiratory syndrome notwithstanding) to managing the inexorable impact of chronic diseases of aging such as heart disease and cancer in our lives. As a consequence, our role as physicians has increasingly evolved into the primary and secondary prevention of the occurrence and consequences of chronic disease. At this time, approximately 5% of the population will develop colorectal cancer during their lifetime; this proportion may increase as the mortality rates from other diseases such as cardiovascular disease are better controlled, since the incidence of colorectal cancer increases exponentially with age. One of the cruel ironies of improving health care is that we increase the proportion of the population that is aging and expose a larger number of people to diseases that are increasingly difficult to prevent or manage. Colorectal cancer is one disease in which intervention is particularly able to alter outcome. Late-stage colon cancer is rarely curable; the earliest stages of colorectal cancer are almost always curable. Early detection of the disease has a dramatic impact on the quality and duration of life. Furthermore, screening leads to the removal of adenomatous polyps, the premalignant lesion, and actually reduces the incidence of cancer. Thus, this is one area in which screening measures have an impact on the quality of life of a population. One would like to find an intervention that would be safe, efficacious, and acceptable to patients. At this time, multiple approaches are available to screen for colorectal cancer (1). The panel of tests includes the fecal occult blood test (FOBT), sigmoidoscopy, barium enema, and colonoscopy. The intent of the health care improvement initiative was to ensure that any type of screening was undertaken; it did not attempt to evaluate the efficacy of any particular method. As pointed out in the article, patient fear, lack of understanding of the tests, and embarrassment all conspire to lead to poor screening compliance. For reasons deeply imbedded in our culture, patients and physicians tend to avoid discussions of bowel function and, generally, patients will do what they can to avoid the interventions necessary to prevent colorectal cancer, even to the detriment of their health. Dr. Stroud and her colleagues have demonstrated that their efforts sharply increased screening from <50% to 86%. All data would suggest that a health benefit is achieved with this. The performance characteristics of the various types of screening tests have recently been reviewed (2). The FOBT would appear to be the simplest and cheapest test, but it has some practical shortcomings. A single FOBT has a low sensitivity (in the range of 30% to 50%), and in order to achieve a 33% reduction in mortality, the test must be performed annually. The mortality reduction is only half this rate if screening is performed every other year. The clinical benefit of this approach is brief, as there is a relatively short window of opportunity when a neoplasm bleeds enough into the bowel to be detected while it is still at a curable stage. Sigmoidoscopy and colonoscopy represent a marked increase in the level of intervention and thus require additional efforts on the part of the primary care physician to convince patients to undertake them; however, their benefits are substantially better. The current evidence suggests that sigmoidoscopy can reduce mortality from colorectal cancer by 70% to 80% in the area of the bowel that is examined. Unfortunately, sigmoidoscopy examines less than half of the colon. It is assumed that colonoscopy detects about 90% of adenomatous polyps and nearly all colorectal cancers; however, this procedure requires an extensive preparation and entails some risks. The best news about screening sigmoidoscopy is that the reduction in mortality is not only robust, but the benefits last for at least 10 years in individuals with a negative exam. Similar data are not available for colonoscopy; however, the difference between colonoscopy and sigmoidoscopy is simply the extent of exam, and it is reasonable to expect a very high level of benefit from colonoscopic screening and removal of all adenomatous polyps. The double-contrast barium enema was historically used to screen for colorectal cancer. However, there has been no prospective study of its impact on reducing cancer mortality, and it is clearly insensitive for the detection of small polyps. A positive test never leads to the removal of a polyp but simply triggers the referral for colonoscopy. Many observers have reasoned that it would be more useful to begin with an endoscopic procedure, either sigmoidoscopy or colonoscopy, rather than to start with an FOBT or a barium enema, both of which are screening procedures for the definitive test, a colonoscopy. Moreover, some have likened the performance of sigmoidoscopy, which examines only the distal half of the colon, to performing mammography on only one breast, the same side, repeatedly (3). What will the future bring? Many efforts are under way to identify screening tests that are more powerful, more acceptable, faster, and cheaper. Abdominal computed tomography (CT) scanning of individuals with a prepped colon that is filled with gas (so-called “virtual colonoscopy”) is currently being evaluated as an alternative screening test. The benefit of this test is that the individual would not need to undergo instrumentation of the colon, and the risks of conscious sedation and possible perforation of the colon can be avoided. However, the patient must undergo the same bowel-cleansing preparation as for colonoscopy, and if there is a positive test, he or she must undergo colonoscopy anyway. At present, approximately 15% of these CT-colonography tests provide false-positive results, which means that the patient must undergo 2 preparations and still have a colonoscopy. The CT approach also will not detect most small polyps. It is unclear whether that is a drawback or a benefit, since many of these tiny lesions can safely be ignored. This technology is rapidly advancing, and one would hope that eventually the CT test could be made highly sensitive, so that most patients who have no neoplasms in their colon could avoid an invasive test. Another new approach currently under investigation is magnetic resonance imaging colonography, but this modality is not likely to be cost-effective. Time will tell. Secondly, stool-based genetic tests are under development. With this approach, a stool specimen is sent to a reference laboratory and DNA is extracted and tested for mutated genes specific for cancer. The test appears to detect about 66% of colorectal cancers and a similar proportion of large adenomas. A small proportion of patients (<10%) have a false-positive test. A number of controlled trials are under way to test the value of this approach. It represents the evolving technologies that have followed on the heels of the molecular biology revolution that began approximately 20 years ago. What have we learned from Dr. Stroud's multidisciplinary health care improvement initiative? First, by increasing the awareness of physicians and patients about the potential benefits of screening for colorectal cancer, the disinterest, fear, and misinformation that currently plague the field can be overcome. Interestingly, when the first attempts were made to screen populations with the FOBT in England, compliance rates were about 37%, despite the use of mass media to alert the public of free testing. The public has also come a long way. It is now commonplace to hear educated persons discussing their recent colonoscopic experiences. Second, by having primary care physicians lead the initiative, the compliance rates were raised to 86%, which is extraordinary and will save lives. Twenty-first–century medicine will require us to take positive steps to bring high-quality care to our patients. We can no longer remain complacent that we are doing our jobs by waiting for our patients to bring their complaints to us. It is very costly in human terms to treat an advanced colorectal cancer, whereas it can take only 20 to 30 minutes to remove a malignant polyp through the colonoscope. One can anticipate the evolution of new techniques that will be more acceptable to patients and will be associated with increased efficacy at lower cost. These technologies need to be evaluated in the full context of their costs. Tests such as the FOBT, barium enema, and CT-colonography are true screening tests, since they lead to the performance of a definitive test (i.e., colonoscopy) when they are positive. Careful analysis of the costs and benefits of going directly to screening colonoscopy at age 50, followed by a rational plan of follow-up in those who either have no lesions in their colon or who have had small polyps removed, may be more cost- effective when the global costs are considered (4). One of the major hurdles to acceptance of colonoscopy or other screening modalities in asymptomatic patients remains the preparation. Currently, little progress is being made in the development of a pleasant, safe way to clean the colon. The bottom line, if you will, is that we should no longer assume that our patients will be persistently noncompliant with regard to colorectal cancer screening. Clearly, the inspired physician can make a difference.