You notice a change in your bowel movements, experience bleeding from the rectum, or notice blood in or on your stool. Don't assume you have hemorrhoids; your doctor will most likely perform a rectal exam, possibly a sigmoidoscopy, or a colonoscopy -- an exam that involves a long flexible tube inserted in your rectum.
You experience persistent abdominal pain, unusual weight loss, or fatigue. These symptoms may be due to other causes, but they could also be linked to cancer.
You are diagnosed with anemia. In determining its cause, your doctor should check for bleeding from the digestive tract because of colorectal cancer.