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Harvard Reports on Cancer Prevention
Volume III: Prevention of Colon Cancer in the U.S.
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Summary
Colon cancer is the third most commonly diagnosed cancer and the second leading cause of cancer-related death in the US. However, it need not occupy such a high rank. Based on our current understanding of the disease, more than 50% of all colon cancers can be prevented through lifestyle changes and widespread screening. To accomplish such a dramatic reduction in incidence, the public health community must facilitate changes in lifestyle and speed the implementation of screening.
The Harvard Center for Cancer Prevention reviewed the current literature on colon cancer to assess the evidence for primary prevention and screening. The report examines the natural history of the disease, modifiable factors that influence its development, and specific screening recommendations. The report also recommends preventive strategies for reducing colon cancer burden in the US.
Natural History of Colon Cancer
Virtually all colon cancers arise from adenomatous polyps (small precancerous lumps that grow on the inner lining of the colon wall). Although these polyps are relatively common, they tend to grow slowly. The transformation of a polyp into cancer usually takes at least 5 years. The extended timeframe of this process provides an excellent opportunity to intervene and prevent the development of malignancy. Intervention strategies include lifestyle changes and routine screening.
Prevention
Nearly 75% of all colon cancer occurs in people without medical risk factors, such as a family history of colorectal cancer, a predisposing genetic syndrome, or a personal history of inflammatory bowel disease. This suggests that most colon cancers can be prevented through lifestyle changes. The report recommends the following behaviors as most effective for lowering the risk of colon cancer, without raising the risk of other complications or diseases:
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Get screened regularly after age 50: Routine screening reduces the risk of dying from colon cancer by at least 33%. Screening tests can detect polyps and remove them before they become cancerous. They can also detect colon cancer early, when treatment is most effective. |
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Be more physically active: Physically active adults are about half as likely to develop colon cancer as sedentary adults. Walking briskly for an hour a day provides the same amount of protection as doing more vigorous activity for 30 minutes a day. |
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Eat less red meat: The more often people eat red meat, the higher their risk of colon cancer. Eating 1 serving per day is associated with a 50% increase in risk |
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Take a daily multivitamin that contains folic acid: Daily multivitamin use for at least 15 years can cut the risk of colon cancer in half. Folic acid is likely to be the key protective nutrient. |
Other behaviors recommended for colon cancer prevention include maintaining a healthy weight, eating more vegetables, limiting alcohol intake, and not smoking.
Screening
A variety of scre ening tests are effective in detecting polyps and colon cancer, including fecal occult blood testing (FOBT), flexible sigmoidoscopy, colonoscopy, and double-contrast barium enema. This report summarizes the evidence for FOBT and flexible sigmoidoscopy. Although colonoscopy and barium enema are effective tests for early detection of polyps and cancers, data are still limited on their use in population-based screening programs.
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Fecal occult blood testing (FOBT) every year: FOBT is inexpensive and non-invasive, though it must be linked with more costly, invasive follow-up procedures for those who screen positive. There is a high rate of false-positives, and the test must be done annually to be effective. Despite its limitations, annual FOBT has been shown to reduce colon cancer mortality by as much as 33%. |
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Flexible sigmoidoscopy every 5 years: Flexible sigmoidoscopy is an invasive procedure that directly visualizes the lower half of the colon. Any growths that are detected can be biopsied and removed during the procedure. People who are screened routinely with sigmoidoscopy may reduce their risk of dying from colon cancer by as much as 50%. In addition, flexible sigmoidoscopy has been associated with a 40% reduction in colon cancer risk. |
Preventive Strategies to Reduce Colon Cancer Burden
Given the rapidly expanding understanding of this disease, the public health community is in an excellent position to develop and implement strategies aimed at preventing colon cancer. These strategies should focus on cultivating an environment that promotes policy initiatives, social norms, and by extension, individual behaviors supportive of health.
Recommended preventive strategies include:
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Making colon cancer prevention a priority and a norm within the health care setting. |
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Implementing employer-based strategies such as Boston Mayor Thomas M. Menino's policy to allow all city employees four hours off each year for cancer screening. |
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Promoting physical activity by restricting downtown urban areas to foot and bicycle traffic and building bicycling and walking paths in all communities. |
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Providing adequate funding to strengthen the nutrition education component of all state health departments. |
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Expanding the number of farmers? markets through collaboration between state Departments of Agriculture, Departments of Public Health, and the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC). |
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