Early detection. Getting a colonoscopy at the appropriate time is the best defense for colorectal cancer. If you are 50, have a family history of colon cancer or polyps or have ulcerative colitis or crohn's disease get a colonoscopy. If you have bleeding or a chnage in bowel pattern see a gi/colorectal doctor to determine if colonoscopy is indicated.
Surgery. Surgical resection remains the most effective therapy for cancers of the intestinal tract.