The colon and rectum are parts of the body’s gastrointestinal system, also called the digestive tract.  After food is digested in the stomach and nutrients are absorbed in the small intestine, the remaining material moves down into the lower large intestine (colon) where water and nutrients are absorbed.  The lower parts of the digestive tract include the rectum and anus, through which stool (solid waste) travels as it passes from the body.

Colorectal cancer (cancer of the colon or rectum) occurs when abnormal cells in the colon or rectum start to divide uncontrollably, forming a malignant (cancerous) tumor.

Cancer cells may invade the healthy tissues around them and spread (metastasize) to other parts of the body such as the liver and lung.  After treatment, some cancers may come back (recur).