About colon cancer

Colon cancer is also known as colorectal cancer. Colon cancer refers to both colon and rectal cancers, which are very similar in terms of risk factors, diagnosis and prognosis. Most people refer to both diseases as colon cancer, which is why we do the same on this website.

As these names suggest, colon cancer is a disease that starts in the cells that line the inside of the colon or the rectum. The colon and rectum make up the large intestine (also called the large bowel), which is part of the digestive system. These organs help break down food, absorb nutrients and pass waste out of the body.

Image of the large intestine

Colon cancer begins when cells in the lining of the colon or rectum change and become abnormal. Abnormal cells can multiply and form small, non-cancerous growths called polyps. Some types of polyps - called precancerous polyps - have the potential to grow into cancer. Precancerous polyps can grow over a long period of time before they become cancer. If you have precancerous polyps you may feel fine and have no symptoms for a long time. Colon cancer screening helps detect polyps early, when treatment can be most effective.

Usually, colon cancer follows a slow and predictable growth pattern. This slow growth lets doctors to detect cell changes at their early stages, when treatment is much more likely to be successful.

If precancerous polyps are removed in their early stages, colon cancer can be prevented.