Colorectal cancer risk factors

Editor(s)-in-Chief: C. Michael Gibson, M.S., M.D. [mailto:mgibson@perfuse.org] Phone:617-632-7753; Elliot B. Tapper, M.D., Beth Israel Deaconess Medical Center

Risk factors
The lifetime risk of developing colon cancer in the United States is about 7%. Certain factors increase a person's risk of developing the disease. These include:
 * Age. The risk of developing colorectal cancer increases with age. Most cases occur in the 60s and 70s, while cases before age 50 are uncommon unless a family history of early colon cancer is present. Cancer in african-americans, however, tends to occur earlier.
 * Polyps of the colon, particularly tubulovillous or villous adenomatous polyps, are a risk factor for colon cancer. The removal of colon polyps at the time of colonoscopy reduces the subsequent risk of colon cancer.
 * History of cancer. Individuals who have previously been diagnosed and treated for colon cancer are at risk for developing colon cancer in the future. Women who have had cancer of the ovary, uterus, or breast are at higher risk of developing colorectal cancer.
 * Heredity:
 * Family history of colon cancer, especially in a close relative before the age of 55 or multiple relatives
 * Familial adenomatous polyposis (FAP) carries a near 100% risk of developing colorectal cancer by the age of 40 if untreated
 * Hereditary nonpolyposis colorectal cancer (HNPCC) or Lynch syndrome
 * Long-standing ulcerative colitis or Crohn's disease of the colon, approximately 30% after 25 years if the entire colon is involved
 * Smoking. Smokers are more likely to die of colorectal cancer than non-smokers.  An American Cancer Society study found that "Women who smoked were more than 40% more likely to die from colorectal cancer than women who never had smoked. Male smokers had more than a 30% increase in risk of dying from the disease compared to men who never had smoked."
 * Diet. Studies show that a diet high in red meat and low in fresh fruit, vegetables, poultry and fish increases the risk of colorectal cancer. In June 2005, a study by the European Prospective Investigation into Cancer and Nutrition suggested that diets high in red and processed meat, as well as those low in fiber, are associated with an increased risk of colorectal cancer. Individuals who frequently ate fish showed a decreased risk. However, other studies have cast doubt on the claim that diets high in fiber decrease the risk of colorectal cancer; rather, low-fiber diet was associated with other risk factors, leading to confounding. The nature of the relationship between dietary fiber and risk of colorectal cancer remains controversial.
 * Research has shown that there is a correlation between red meat and colon cancer, but there is not a risk associated with white meat, therefore it is hypothesized that it is heme iron that may cause the colon cancer. It is also important to distinguish between heme iron and non-heme iron, which is found in fruit juice, cereals, and bread. Heme iron, which is found in red meat, is hypothesized to catalyze the formation of endogenous NOCs (N-nitroso compounds). Many NOCs are carcinogens and studies have shown that an increase in NOCs are caused by red meat and not from isolated proteins from foods such as vegetables.
 * Virus. Exposure to some viruses (such as particular strains of human papilloma virus) may be associated with colorectal cancer.
 * Alcohol. See the subsection below.
 * Primary sclerosing cholangitis offers a risk independent to ulcerative colitis
 * Low selenium.
 * Inflammatory Bowel Disease. About one percent of colorectal cancer patients have a history of chronic ulcerative colitis. The risk of developing colorectal cancer varies inversely with the age of onset of the colitis and directly with the extent of colonic involvement and the duration of active disease. Patients with colorectal Crohn's disease have a more than average risk of colorectal cancer, but less than that of patients with ulcerative colitis.
 * Environmental Factors. Industrialized countries are at a relatively increased risk compared to less developed countries or countries that traditionally had high-fiber/low-fat diets. Studies of migrant populations have revealed a role for environmental factors, particularly dietary, in the etiology of colorectal cancers. Genetic factors and inflammatory bowel disease also place certain individuals at increased risk.
 * Exogenous Hormones. The differences in the time trends in colorectal cancer in males and females could be explained by cohort effects in exposure to some sex-specific risk factor; one possibility that has been suggested is exposure to estrogens . There is, however, little evidence of an influence of endogenous hormones on the risk of colorectal cancer. In contrast,there is evidence that exogenous estrogens such as hormone replacement therapy (HRT), tamoxifen, or oral contraceptives might be associated with colorectal tumors.

Alcohol
On its colorectal cancer page, the National Cancer Institute does not list alcohol as a risk factor : however, on another page it states, "Heavy alcohol use may also increase the risk of colorectal cancer"

The NIAAA reports that: "Epidemiologic studies have found a small but consistent dose-dependent association between alcohol consumption and colorectal cancer even when controlling for fiber and other dietary factors.   Despite the large number of studies, however, causality cannot be determined from the available data."

"Heavy alcohol use may also increase the risk of colorectal cancer" (NCI). One study found that "People who drink more than 30 grams of alcohol per day (and especially those who drink more than 45 grams per day) appear to have a slightly higher risk for colorectal cancer." Another found that "The consumption of one or more alcoholic beverages a day at baseline was associated with approximately a 70% greater risk of colon cancer."

One study found that "While there was a more than twofold increased risk of significant colorectal neoplasia in people who drink spirits and beer, people who drank wine had a lower risk. In our sample, people who drank more than eight servings of beer or spirits per week had at least a one in five chance of having significant colorectal neoplasia detected by screening colonoscopy.".

Other research suggests that "to minimize your risk of developing colorectal cancer, it's best to drink in moderation"

Drinking may be a cause of earlier onset of colorectal cancer.