What Causes Colorectal Cancer?

Cancer of the colon and rectum develops when the growth rate of one type of cell in the large bowel gets out of control, continuing to divide even when new cells aren't needed. This exaggerated growth can cause precancerous polyps (an abnormal growth of tissue projecting from a mucous membrane) to form in the lining of the intestine. Over a number of years, these polyps may become cancerous, penetrating the colon walls and spreading to lymph nodes and other organs.

Polyps may form anywhere in the large intestine, either in the colon (the upper 120-150 cm) or in the rectum (the lower 20-25 cm).

Types of Polyp

There are a number of different types of polyps, including the following:

1. Adenomas

A collection of growths that are commonly found during colonoscopy. They are usually removed during screening tests because of their tendency to become malignant.

2. Hyperplastic Polyps

A generally harmless form of polyp, which is rarelya risk factor for colorectal cancer.

3. Inflammatory Polyps

A group of polyps that tend to form after a bout of ulcerative colitis. They may become cancerous.

Risk Factors

Although bowel cancer may develop at any age, the majority of cases occur in people over the age of 50. However, there are a number of other factors that may increase the risk of contracting this disease.

• Having a family member that has contracted the disease
• Diets low in fibre and high in fat and calories
• High alcohol intake
• Inflammatory disease of the colon, such as Crohn's disease or ulcerative colitis
• A sedentary lifestyle (waste stays in the colon longer in inactive people)
• Diabetes (diabetics have a 40% increased risk)
• Smoking (not only can smoking cause cancer, but once diagnosed, smokers also face a 40% increased risk of dying of the disease)
• Familial adenomatous polyposis (FAP) - a rare hereditary disease that causes hundreds of polyps to develop in the colon and rectum
• Ashkenazi Jews (1 in 10 Ashkenazi Jews carry a faulty gene that may increase the tendency of bowel cancer)
• Hereditary nonpolyposis colorectal cancer (HNPCC) -a hereditary disorder that can increase the risk of developing colon cancer or rectal cancer at an early age