PubMed1996
Chemoprevention refers to the use of specific natural or synthetic chemical agents to reverse, suppress, or prevent the progression to invasive cancer. The ideal chemopreventive agent is safe and nontoxic over the long term. It should be easy to take and demonstrated to be effective in randomized trials in humans. Aspirin and NSAIDs meet many of the criteria for an ideal agent. The literature on aspirin and NSAIDs makes it clear that these agents can prevent colorectal cancer and precursor adenomas. That does not mean that we should make general recommendations for their use. First, we do not know the proper dose or duration. More important, these medications are accompanied by adverse effects that can be considerable. Indeed, the Medical Letter, an authoritative, unbiased publication on drugs and therapeutics, concluded that "for primary prevention in low-risk patients, more studies are required to establish whether the beneficial effect of aspirin is great enough to compensate for the possible increased risk of hemorrhagic stroke." These recommendations were directed at the use of these medications for prevention of myocardial infarction, but the same conclusions apply to colorectal cancer: although aspirin may prevent the disease, it may increase the risk of hemorrhagic strokes or cause other adverse effects. We must accurately balance the benefits and risks of these drugs, based on the results of ongoing randomized studies, before recommending aspirin for prevention of colorectal cancer. Is there anything that we can recommend to our patients for prevention of colorectal cancer? Based on observational epidemiologic studies, it is clear that individuals who consume a diet high in vegetables and natural fibers and low in fat have a reduced risk of colon cancer and polyps. Optimal nutrient intakes for the prevention of cancer might be more readily achieved via food fortification or supplementation, but this requires more research. Regular physical exercise and maintenance of normal body weight are also protective. Until the results of definitive studies of chemopreventive agents are available, we can recommend that our patients eat a sensible diet, exercise, and avoid obesity. Such an approach should protect them from cardiovascular disease, an even deadlier condition than colorectal cancer. In the future, we need randomized prevention trials that, for logistic reasons, may need to focus on the occurrence and progression of colorectal adenomas rather than carcinoma itself. Studies that test more than one compound at a time, using factorial designs, will be more efficient. We will need better information about duration and dose, adverse side effects, molecular mechanisms, and cellular sites of NSAID activity. Ultimately, we will need to know more about the biology and molecular biology of colorectal cancer and its precursors. That information will, perhaps, permit us to design agents to interrupt the pathway to cancer and to use intermediate markers more intelligently.