Genetic Factors

Heredity is perhaps the strongest risk factor for developing colorectal cancer. It is estimated that approximately 20% of all cases of colorectal cancer are hereditary. This risk increases if you have a primary relative, such as a parent, sibling, or child who develops colorectal cancer.

Hereditary colon cancer occurs at a younger age. As a result, anyone with a history of colon cancer in a relative should seek screening early. Guidelines recommend a screening at age 40 or 10 years younger than the earliest age at which a relative developed colon cancer, whichever is younger. Even in the absence of hereditary nonpolyposis colon cancer (HNPCC) and familial adenomatous polyposis (FAP), the presence of the disease before age 60 in near relatives increases one’s own risk.

The two most common forms of inherited colon cancer are:

• Hereditary nonpolyposis colon cancer (HNPCC)—This is a fast-growing form of colorectal cancer. It accounts for about 5-15% of all colorectal cancer cases. Typically, people with this form develop cancer in their 40s.
• Familial adenomatous polyposis (FAP)—People with this type of colorectal cancer develop hundreds of polyps at a very young age, sometimes as early as their teens. Initially, polyps are benign but do become cancerous over time. This type of colorectal cancer is rare. It only occurs in 1% of all colon cancer cases. If you have these polyps, the likelihood that you will develop colon cancer is almost 100%. Many patients have most of their colon removed as a preventive measure.

Age

Colorectal cancer most commonly occurs after age 50, though certain forms of this cancer may develop earlier. However, colorectal cancer can occur at any age.

Lifestyle Factors

Colorectal cancer has been strongly associated with lifestyle factors. The following factors may increase your risk of developing colorectal cancer:

• Diet—Diets high in fat, particularly fat from animal sources, and low in fiber have been associated with increased risk of colorectal cancer. Eating a diet that is high in fruits and vegetables may help lower the risk.
• Lack of exercise—Regular exercise has been shown to decrease the risk of developing colorectal cancer. Even moderate exercise of 30 minutes per day is beneficial.
• Obesity—Obesity increases the risk of colorectal cancer, particularly when weight is distributed in the waist, rather than on the hips and thighs.
• Smoking—Smokers are at increased risk of getting colorectal cancer and dying due to colorectal cancer than nonsmokers.
• Alcohol—Three or more alcoholic beverages a day increases risk of colorectal cancer. Drinking alcohol is also associated with a higher risk of forming large benign tumors called colorectal adenomas.

Gender

Although both men and women develop colorectal cancers, men are at a higher risk.

Medical Conditions

The following medical conditions have been shown to increase the risk of developing colorectal cancer:

• Ulcerative colitis and Crohn’s disease
• Polyps
• Previous colorectal cancer