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. With inherited forms of colon cancer, the presence of the disease before age 60 in near relatives increases one’s own risk.

The 2 most common forms of inherited colon cancer are:

• Lynch syndrome —This is a fast-growing form of colorectal cancer. It accounts for about 5% 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. The likelihood of colon cancer is almost 100% by age 40. Many opt to have most or all of their colon removed as a preventive measure.

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 are associated with an increased risk of colorectal cancer. Eating a diet that is high in fruits and vegetables may help lower the risk.
• Lack of exercise —A sedentary lifestyle increases the risk of colorectal cancer. Even moderate exercise of 30 minutes per day is beneficial.
• Smoking—Smokers are at increased risk of getting colorectal and other cancers. The risk of dying from colorectal cancer is also higher for smokers than nonsmokers.
• Alcohol—Three or more alcoholic beverages a day increases risk of colorectal cancer.

Medical Conditions

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

• Ulcerative colitis and Crohn disease—Infection and irritation cause cell changes in the wall of the colon and rectum.
• Colon polyps —Abnormal growths can sometimes turn into cancer if left untreated.
• Previous colorectal cancer —Cancer can recur in new areas of the colon and rectum even if a tumor was surgically removed. The earlier in age you had colorectal cancer, the more likely it is to come back.
• Type 2 diabetes—People with type 2 diabetes have a higher risk of colorectal cancer. Diabetes is also be associated with negative outcomes during and after treatment.
• Obesity—Obesity increases the risk of colorectal cancer, particularly when weight is distributed in the waist, rather than on the hips and thighs.

Race and Ethnicity

African-Americans carry the highest risk of developing and dying from colorectal cancer.

Ashkenazi Jews are at an increased risk because of a specific genetic mutation.