Risk Factors
Colorectal cancer is the third most common cancer in the U.S., with Americans facing a lifetime chance of 5.5 - 6% for this cancer. In 2005, colorectal cancer was expected to cause 145,290 new cases and 56,290 deaths in the United States. About 72% of cancers occur in the colon and 28% in the rectum.
Sex
The lifetime risk of cancer of the colon or rectum is 5.9% for men and 5.5% for women.
Age
Colorectal cancer risk increases with age. More than 90% of these cancers occur in people over age 50. The rate of colorectal cancer in patients under 20 years is less than 1 in 100,000 per year. At age 50 about one in 2,000 people per year will develop colorectal cancer. After age 65, this rate increases to almost 3 in 1,000.
Ethnicity
African Americans have the highest risk of being diagnosed with, and dying from, colorectal cancer. Among Caucasians, Jews of Eastern European (Ashkenazi) descent have an elevated rate of colorectal cancer. Asian Americans/Pacific Islanders, Hispanics/Latinos, and American Indians/Alaska Natives have a lower risk than Caucasians. In all ethnic groups, men have a higher risk than women.
Family History
About 20 - 25% of colorectal cancers occur among people with a family history of the disease. (Seventy-five percent of cases are due to other causes.) People who have more than one first-degree relative (sibling or parent) with the disease are especially at high risk. The risk is even higher if the relative was diagnosed with colorectal cancer before the age of 60.
About 5 – 10% of patients with colorectal cancer have an inherited genetic abnormality that causes the disease. Genetic mutations associated with colorectal cancer include familial adenomatous polyposis (FAP) and hereditary nonpolyposis colorectal cancer (HNPCC).
Lifestyle Factors
The risks for colon cancer are far higher in industrialized nations than less developed countries. A Western lifestyle, being sedentary, smoking, and excess weight have all been associated with increased risk for colorectal cancer. (It should be noted, however, that about 75% of cases occur without a known predisposing factor.)
Dietary Factors. A diet high in red meat consumption increases the risk for colorectal cancer. Other types of animal protein (low-fat dairy products, fish, poultry) may decrease the risk of developing polyps and colorectal cancer. Studies on fruits, vegetables, and fiber are mixed. There is some evidence that diets very low in fruits and vegetables may increase the risk. In any case, eating a variety of fruits and vegetables should be part of a healthy diet.
Alcohol and Smoking. Alcohol use and smoking increase the risk for colorectal cancer. Patients who smoke and drink may also be diagnosed with colorectal cancer at a younger age than non-drinkers and non-smokers. Several studies suggest that women who smoke are at especially high risk of developing colorectal cancer.
Obesity. There is a demonstrated link between body mass and colon cancer risk for both men and women. The Centers for Disease Control and Prevention has reported that the risk of colon cancer rises as body mass index (BMI) increases. Obesity has been associated biologically with higher circulating levels of insulin and a hormone called insulin-like growth factor (IGF). Chronically high levels of these substances may increase colorectal cancer risk.
Physical Inactivity. More than 50 studies from around the world suggest that physical activity helps prevent colon cancer. In contrast, exercise does not protect against rectal cancer.
Risk Factors for People with Inflammatory Bowel Disease
Crohn's disease and ulcerative colitis are chronic afflictions of the large intestine known as inflammatory bowel diseases (IBDs). Both have been linked to increased risk for colorectal cancer. (Patients with ulcerative colitis have a higher risk than those with Crohn's disease.) Family histories are helpful in determining risk associated with inflammatory bowel disease. Some studies suggest the following:
- Patients with IBD who have a family history of colorectal cancer face up to a five-fold risk of colon cancer themselves.
- Individuals without IBD who have relatives who suffered from both IBD and colorectal cancer may face a higher risk for developing colorectal cancer themselves.
- Individuals without IBD but with a family history of IBD and no colon cancer most likely face no higher risk for cancer themselves.
Other Risk Factors
Polyps. Polyps are tissue growths, usually benign, that develop in the color or rectum, most often in patients over 50 years of age. When pathologists examine polyps removed from the colon, they classify them as either hyperplastic or adenomatous. Both types are benign, but some adenomas will become malignant. As a preventive measure, polyps should be removed (polypectomy).
Ureterosigmoidostomy. People who have had ureterosigmoidostomy, a surgical procedure to correct a birth defect in the bladder or to treat some bladder cancers, may develop tumors near the site of the defect, which is chronically exposed to urine and feces. Such patients have a 5 - 10% chance of developing colon cancer 15 - 30 years after the operation.
Diabetes. Many studies have identified an association between type 2 diabetes and colon cancer. Both diseases share common risk factors of obesity and physical inactivity, but diabetes itself is a risk factor for colorectal cancer. Data from a case control study of 50,000 U.S. veterans presented at the 2004 Digestive Disease Week conference found that patients with diabetes were 32 percent more likely to develop colon cancer than similar patients who did not have diabetes. Both men and women who have diabetes are at risk.
Heart Disease. Coronary artery disease (CAD) increases the risk for colorectal cancer. Both CAD and colorectal cancer share important risk factors, including smoking, high fat diet, sedentary lifestyle, and obesity.
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