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.

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.

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

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

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