The exact reason why colorectal cancer develops on a person is unknown. There are several factors, which promote the development of colorectal cancer. Some of these factors are modifiable like diet habits while other like age and race are un-modifiable factors.
Environmental factors that promote colorectal cancer
People do migrate from country to country and once they migrate from a lower colon cancer risk areas of the world to higher risk areas of world they tend to acquire the risk of the country to which they are migrating. These findings suggest the presence of environmental factors causing higher risk of developing colorectal cancer.
Smoking and alcohol consumption
Smoking and drinking alcohol or more than one drink per day were shown to increase the risk of developing colorectal cancer.
Intake of fatty diet and consumption of animal fat are known to cause increased risk of development of colorectal cancer. Intake of red meat has been recently shown to increase the risk of colorectal cancer. Intake of diet high in cholesterol also has also been associated with increased risk of development of colorectal cancer. It is thought that increased consumption of dietary fat causes increased production of secondary bile acids, and related compounds including steroids. The increased bacterial breakdown of these secondary bile acids, and steroids probably results in production carcinogens (cancer causing chemicals) thus increasing the risk of developing colorectal cancer. Several types of food have been suggested to have protective effect on colon cancer. These include food rich in fiber, yellow and green vegetables diets containing high calcium contents. There is not much scientific proof to substantiate many of these claims.
Inflammatory bowel diseases including ulcerative colitis, and crohn's disease cause increased risk of developing colorectal cancer. With regard to ulcerative colitis, the risk of development of colorectal cancer is related to the duration since the diagnosis of ulcerative colitis, extent of involvement and presence of abnormal cells at the site of disease. Risk of developing colorectal cancer increases markedly with the duration of colitis, with a risk of approximately 3 percent for colitis up to 10 years duration increasing to 20 percent if the duration increases to 20 years.
Adenomatous polyps in the large intestine
Patients who were found to have adenomatous polyps in the colon during a colonoscopy have a higher chance of developing colorectal caner compared to those who have no polyps. If an adenoma is detected in the colon there is a 3 percent chance that this may be harboring a malignancy. Polyps, which show histology of villous adenoma, have a higher risk of progressing into colorectal cancer. The risk is also depended on the size of the polyp. If a villous adenoma has a size of less than one centimeter the risk of development of colorectal cancer is about 3 percent, where as the risk would be 40 percent if the polyp size is more than 2 centimeters.
Prior history of cancer
Patients who have been diagnosed with colorectal cancer and have been successfully treated, have a higher risk of developing a second primary colon cancer. Women who had a previous diagnosis of breast cancer, endometrial cancer, or ovarian cancer may have increased risk of developing colorectal cancer.
There are several hereditary disorders that are associated with increased risk of developing colorectal cancer. This include familial adenomatous polyposis (FAP), hereditary non-polyposis colorectal cancer (HNPCC) and several other less known genetic disorders.
Genetic risk factors for colon cancer