The exact reason why colon cancer develops in some persons and not in others is not clear. The incidence of colon cancer is quite varied among different countries and within different ethnic groups inside the same country. Industrialized countries like United States, Canada, UK, Western Europe, Australia and Japan have a much higher incidence of colorectal cancer compared to the less industrialized parts of the world like Asia, Africa, and South America. Colorectal cancer represent over 9 percent of all cancers in men and about 10 percent of all cancers in women world-wide. In industrialized countries the incidence of colorectal cancer can be as high as 12 to 14 of all cancers, and in non-industrialized countries much lower rates of about 7 to 8 percent of all cancers diagnosed may be colorectal cancer.

Excluding skin cancer, colorectal cancer is the third commonest cancer diagnosed in the United States. Each year over 100,000 Americans are diagnosed with colon cancer and over 50 percent of these patients will die from colorectal cancer. Colon cancer incidence is not much different between males and females, however colon cancer is slightly more prevalent in women compared to men (ratio of 1.2:1) but the rectal cancer is more common in males (ratio of 1.7:1).

Even though we do not know the exact cause of development of colorectal cancer, scientists have recognized several factors that can increase the risk of development of colorectal cancer. A risk factor for a disease is any condition that makes a person more likely to develop that diseases. Some of the risk factors like dietary factors are modifiable by the person involved while some other factors like age are un-modifiable. These risk factors may act in combination, and this combination of risk factors may be associated with cumulative increase in the risk of development of colorectal cancer. The simple presence of one or more risk factors does not necessarily mean that someone will develop colorectal cancer. On the other hand absence of all risk factors does not mean that an individual will not develop colorectal cancer, but generally more risk factors you have higher is the chance of developing colorectal cancer. Environmental factors also may be playing a role in the development of colorectal cancer. People who migrate from areas of low risk to areas of the world with higher risk of developing colorectal cancer, they tend to acquire the risk of the country to which they are migrating. This finding suggests the presence of environmental factors causing higher risk of developing colorectal cancer. Changes in dietary factors associated with migration may also be contributing to this increase in risk associated with migration from low risk areas to higher risk areas.

Risk factors for the development of colorectal cancer include the following:

• Age over 50 years
• Increased fat intake
• Large intestinal polyps
• Family history of colon cancer
• Inflammatory bowel diseases like ulcerative colitis and Crohn's disease.
• Personal history of other cancers
• Sedentary habits and lack of exercise
• Obesity
• Diabetes
• Smoking
• Alcohol content
• Genetic colon cancer syndromes like Familial adenomatous polyposis or Hereditary Non-polyposis Colon Cancer (HNPCC)