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Causes of colon and rectal cancer

Environmental factors and genetic factors have been found to cause colorectal cancer.


Genetic causes

Familial Adenomatous polyposis is an inherited condition where multiple polyps develop in the colon during childhood. They usually cause symptoms by the age of 16 and if left untreated will develop into cancer in most cases across the next 20 years. The condition is caused by a mistake in a gene, called the 'adenomatous polyposis coli gene'.


Hereditary nonpolyposis colorectal cancer, also called  the 'Lynch Syndrome', is a genetic condition that causes colorectal cancer at a younger thatn norma age, and tends to affect the first half of the colon. Multiple polyps are not present.  The condition is also associated with an increased risk of cancers of the ureter, pancreas, bile ducts, small bowel, stomach, ovary and womb.


Other risk factors

A diagnosis of Ulcerative Colitis:

Patients with Ulcerative Colitis have an icreased risk of colon cancer, particulary if the whole colon is affected. If patients have 'primary sclerosing cholangitis' as well, the risk is increased further.


A Diagnosis of Insulin Dependent Diabetes:

It has been found that this diagnosis can multiply the risk of developing colon cancer by a factor of 1.3.


Alcohol consumption

This increases the risk of cancer of the colon and rectum significantly if more than 3 or 4 units of alcohol are taken a day.


Being Overweight

Being very overweight increases the risk of colorectal cancer by 50%.



Active smoking (as opposed to passive smoking) seems to increase the risk of rectal cancer.



Eating plenty of fruit and vegetables may be protective against colorectal cancer and red meat may increase the risk. However, there is some doubt as to whether this is really true. The role of fibre and folic acid as protective factors is also controversial although garlic and eating oily fish have been show to help.



Aspirin, Hormone Replacement Therapy, and Statins (used for lowering cholesterol) may reduce the risk of colorectal cancer.

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