Colon and Rectal Cancers

Description

Alternative Names

Risk Factors

Colorectal cancer is the fourth most common cancer in the US, with Americans facing a lifetime risk of 6% for this cancer. An estimated 147,000 people in the US are expected to be diagnosed with colon or rectal cancer in 2004.

Sex

The risks overall are equal in men and women, but men have a higher risk for rectal cancers and women for colon cancers.

Age

The most important risk factor for colon cancer is getting older. More than 90% of these cancers occur in people over 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, and after age 65, this rate increases to almost 3 in 1,000.

Ethnicity

Compared to Caucasians, African Americans are at higher risk of colon (but not rectal) cancer. The highest risks are in men of African descent, particularly in the sub-Saharan region. Ashkenazi Jews, of Eastern Europe descent, also have a higher incidence of colorectal cancer.

Family History

About 25% of patients under 45 years old and 15% of everyone who develops colorectal cancer have a genetic risk. The average lifetime risk of developing colorectal cancer is approximately 2%. People who have a sibling or parent (first degree relative) who developed colorectal cancer have three times (6%) the lifetime risk of developing colorectal cancer. People who have a first degree relative who developed colorectal cancer before age 45 have an even higher, 10%, lifetime risk of developing colorectal cancer.

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. Studies indicate that diets low in fruits and vegetables and high in meats pose a risk for colon cancer. Research also indicates that diets rich in fruits and vegetables are protective against many cancers.

Alcohol and Smoking. Smoking may increase the risk for colon cancer, and drinking alcohol regularly appears to compound this risk. Nonsmokers who drink alcohol and have diets rich in vegetables and fruits do not seem to have an increased risk.

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

Crohns 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. 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.

Crohn's disease, also called regional enteritis, is a chronic inflammation of the intestines which is usually confined to the terminal portion of the small intestine, the ileum. Ulcerative colitis is a similar inflammation of the colon, or large intestine. These and other IBDs (inflammatory bowel disease) have been linked with an increased risk of colorectal cancer.

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% to 10% chance of developing colon cancer 15 to 30 years after the operation.

Diabetes. Many studies have identified a possible association between type 2 diabetes and colon cancer. Both diseases share common risk factors of obesity and physical inactivity, but diabetes may independently predispose for colon 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.