The bad news: colon cancer is a killer. The disease is responsible for approximately 48,000 deaths in the United States each year, making it the second leading cause of cancer death in the country.
The good news: more than half of colon cancers can be prevented through lifestyle changes and routine screening.
“Weve reviewed what is known about colon cancer,” said Graham Colditz, director of education for the Harvard Center of Cancer Prevention. “And what we found is that this killer is remarkably preventable through fairly easy changes in diet and physical activity, and through regular screening.” Details on prevention measures, in addition to a discussion of the burden of cancer in the United States, are found in the “Harvard Report on Cancer Prevention, Volume 3: Prevention of Colon Cancer in the United States,” printed in the June 1999 issue of Cancer Causes and Control.
Colon cancer occurs when cells in the colon, the upper five to six feet of the large intestine, grow out of control. Virtually all colon cancers begin as small noncancerous tumors called adenomatous polyps. These polyps are relatively common, found in 25 percent of Americans by age 50, with increasing prevalence as people age. Over the course of time about 10 to 15 years some of these polyps may transform and become cancerous.
“The 10- to 15-year time frame of the adenoma-carcinoma sequence provides us with a valuable opportunity to intervene on risk factors and prevent the development of malignancy,” write the authors in the report.
“The number one risk factor for colon cancer is lack of physical activity,” said Colditz. “By itself, high levels of physical activity might decrease risk of colon cancer by as much as 50 percent.”
While maintaining a high level of physical activity throughout life imparts the greatest protection, anti-cancer benefits have also been found for those reporting lower levels of activity, and even for those who only began to exercise later in life. “The messages here are that, as far as physical activity is concerned, more is better, some is better than none, and its never too late to start,” said Colditz.
Several dietary habits that influence peoples risk for colon cancer include eating red meat (increases risk), use of multivitamins containing folic acid (reduces risk), and high intake of vegetables (evidence is weak, but a protective effect seems likely).
“In addition to lowering the numbers of colon cancer patients through changes in exercise and eating habits,” said Colditz, “we can reduce the suffering and death caused by this disease through screening tests.” Two tests have been recommended by the U.S. Preventive Services Task Force and reviewed in the Centers report. The tests are the fecal occult blood test and the flexible sigmoidoscopy procedure.
Widespread use of these tests would reduce colon cancer morbidity through two mechanisms: first, they would allow for the detection and removal of precancerous polyps. Second, colon cancer in its early stages is treatable screening tests would allow physicians to diagnose colon cancer before it is necessarily deadly.
The risk of dying from colon cancer is reduced by more than a third for people over age 50 who get screened regularly. This risk reduction may be even greater for the small percentage of people (estimated to be less than 10 percent of the population) at high risk due to inheritance of a mutation in one of the half-dozen genes that specify predisposition to colorectal cancer.
Two other screening tests, colonoscopy and barium enema, are also effective and may be recommended by physicians.
In addition to the annual Harvard Report on Cancer Prevention, the Center is also targeting colon cancer reduction through multiple communications efforts. Partnering with the Massachusetts Colorectal Cancer Working Group, the center has developed, printed, and distributed a brochure explaining colon cancer prevention to physicians offices. The brochure is intended for physicians to distribute to patients, both giving patients valuable information and opening a dialogue about colon cancer between the patient and physician.
The Center also takes its message of cancer prevention to the world thorugh the School of Public Healths Website at http://www.hsph.harvard.edu, where the visitor can link up to the Colon Cancer Risk Index. The Index is a project that allows Web surfers to answer an interactive questionnaire and discover an approximation of their risk level for colon cancer and, more importantly, what they can do to reduce their risk. An expanded, interactive cancer prevention site has just been launched.