The colon and rectum are parts of the body's digestive system. The digestive system consists of a group of organs where the food is processed to create energy and the waste material is stored until it passes out of the body as stool. Together, the colon and rectum form a long, muscular tube called the large intestine. The colon is the first 6 feet of the large intestine, and the rectum is the last 8 to 10 inches.

Cancer occurs when cells in a part of the body begin to grow out of control. This uncontrollable growth of abnormal cells crowds out the normal cells and replaces them. The walls of the colon and rectum have several layers of tissues. Colorectal cancer begins in the innermost layer and slowly spreads to the other layers as the disease progresses.

Cancer cells can sometimes break away from a tumor and spread to other parts of the body through the blood or lymph system. Cancer that has spread in this way is called metastatic cancer. When cancer comes back in a person who appeared to be free of the disease after treatment, it is called a recurrence.

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Quiz on Cancer