Colon Polyps (cont.)
Bhupinder Anand, MD
In this Article
Are all colon cancers associated with polyps?
No, although most colon cancers arise from polyps, some do not. Some arise within the wall of the colon. These cancers may be flat or even depressed (excavated). They are more difficult to identify and treat, and they are more likely to spread into the wall of the colon and nearby lymph nodes than cancers originating in polyps. This is particularly true of serrated adenomatous polyps which usually are flat rather than polypoid in appearance.
There also is a familial, genetic syndrome called hereditary nonpolyposis colorectal cancer (HNPCC, Lynch syndrome) in which colon cancers occur with very high incidence (80% or more of patients). There are few or no polyps to identify in these patients. Moreover, the cancers occur at a younger age, often prior to the time screening for colon cancer is recommended to begin, and the syndrome is not recognized until a family member develops cancer usually at a young age. HNPCC is suspected because other family members also have colon cancer and certain criteria are met (Amsterdam or Bethesda criteria), or the cancer shows a particular pattern under the microscope with special stains. If HNPCC is suspected, genetic testing on the cancer can be done to identify the hereditary mutation, and other family members can be tested for the same mutation. If present, the family members can begin screening colonoscopies. HNPCC may be associated with cancers in tissues outside the colon as well. Fortunately, HNPCC is responsible for only a few percent of all colon cancers.
Can colon polyps be prevented?
Because of concern regarding the transition of polyps to cancer, attempts have been made to determine if treatments with theoretical potential actually prevent polyps. The problem with most studies is that they are retrospective, observational studies which are not sufficient as proof. The long period of time (many years) that it takes for polyps to form makes long term studies mandatory, but such studies have been difficult to do except in the case of familial, genetic polyposis syndromes, and, because of the differences in their causes, it is not clear if what applies to them applies to the more common sporadic adenomas.
Several associations have been explored for antioxidants including selenium, beta carotene, and vitamins A, C, and E. Most of the studies that have been done do not support a role for these agents in preventing polyps or in preventing colon cancer. A limited amount of support is available for the use of selenium to prevent polyps, but selenium is not recommended for use outside of experimental trials.
Supplemental dietary calcium has been demonstrated in one study to prevent the formation of polyps. The benefit was seen with supplementation of 1200 mg of calcium. There is some concern about using calcium since higher dietary and supplemental levels are associated with an increase in vascular disease. The intake of calcium that was studied was higher than the recommended intake of calcium, 800 mg.
The best support for a treatment to prevent polyps is with nonsteroidal anti-inflammatory drugs (NSAIDs), a class of drugs that includes aspirin, ibuprofen (Motrin, Advil), celecoxib (Celebrex), and many others. Aspirin has been shown in several studies to reduce the formation of polyps by 30% to 50%. The effect is likely to occur with higher doses of aspirin (more than the 81-325 mg that is recommended for cardiovascular disease prevention), and there is concern about aspirin's side effect of gastrointestinal bleeding at these doses.
Celecoxib (Celebrex), a "COX-2 selective NSAID" has been shown to reduce colon polyps 30% to 50% as well, but there is a lingering concern about the possible cardiovascular side effects that may be seen with most NSAIDs (though the data supporting this side effect is conflicting). It may be used in patients genetic polyposis syndromes who choose not to have their colons removed. Celecoxib might be considered in patients with a low risk for cardiovascular disease who develop adenomatous polyps frequently.
Sulindac (Clinoril), a "non-selective NSAID" has been shown to prevent polyps in patients with sporadic adenoma as well as the genetic syndromes. As with celecoxib, there is concern about cardiovascular side effects.
Given the information that is available, it is not recommended that patients at average risk for the formation of additional polyps be treated for prevention because of concern that the risks of treatment, primarily intestinal bleeding and cardiovascular disease, may outweigh the benefit of polyp prevention. It may be reasonable to treat patients who are at higher than average risk for polyps in whom the benefit may outweigh the risks. Such patients might include those with frequent polyp formation, particularly those who have demonstrated cancerous changes in the polyps, or patients who already have had colon cancer. Studies in these types of patients are eagerly awaited.
Reviewed by Bhupinder Anand, MD on 3/15/2013
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