An abnormal growth of cells that starts in the lining of the colon (large bowel) and, if not removed, will continue to grow and spread to other parts of the body.

HOW IS COLON CANCER DIAGNOSED AND TREATED?  

Colon caner is usually identified on sigmoidoscopy or colonoscopy. This involves inserting a lighted instrument into the rectum to inspect the lining of the lower bowel. The treatment of colon cancer is usually surgery and involves the removal of the portion of large bowel that contains the cancer.

"Bleeding from the rectum is always due to hemorrhoids."

Actually, bleeding from the rectum, whether bright red or dark maroon, can be the first sign of colon cancer and should always be evaluated by a physician.