If a cancer in the colon is causing symptoms, it probably already has been present for some time, since very small cancers usually don’t cause any problems.  And so, we really want to find these cancers before they cause symptoms.  This means that we must look for polyps and cancers in people who have no evidence of cancer.  We try to focus on those who at least statistically are more likely to develop colon or rectal cancer.  This is the reasonwe recommend colonoscopy for patients once they turn 50, because these cancers are more common as you get older.  For African Americans, screening is recommended to begin at age 45 or even earlier, because the incidence is higher.  And if you have a family history of cancer, screening should begin earlier.

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Even though screening is our primary recommendation for diagnosing colorectal cancer, there are going to be patients who have symptoms before a cancer is found.  If you have any of these symptoms, it does not necessarily mean you have colon cancer, but you almost certainly should be checked for this possibility.


There can be a change in your usual bowel habits.  If you typically have bowel movements “like clockwork” every morning, or twice a day, or every other day, and then you start having more or less frequent bowel movements, perhaps sometimes diarrhea and sometimes hard, or if you notice that the stools start coming out real “thin”, like the thickness of pencil, or if you just become more constipated, these symptoms should be evaluated, since sometimes they occur because of a cancer.

Rectal bleeding should always be taken seriously to determine the cause.  Bleeding might be noted simply as some blood on the toilet paper when you wipe after a bowel movement.  It might be noted as a pinkish tinge to the water in the toilet bowl after a bowel movement.  You might notice blooding dripping from your rectum near the end of bowel movement.  You might notice blood clots mixed in with the stool, or what looks like streaks of blood on the surface of the stools.  Blood that has come from higher up in the intestinal tract may be altered, so that it looks maroon, or even black (this is called melena). In any of these cases, you should contact your doctor to determine the source of the blood.  There are a number of different possible explanations, including hemorrhoids, anal fissures, benign polyps, diverticulosis, ulcers, inflammatory disease of the intestines, malformations of the vessels in the bowel, or various types of cancer.

The other signs and symptoms listed are less specific for the possibility of colon cancer, such as abdominal pain, weakness and fatigue, or unexplained weight loss.  But such symptoms should be discussed promptly with your doctor to determine the cause.

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Suggested next pages

Etiology of Colon Cancer

Diagnosis of Colon Cancer

Treatment of Colon Cancer

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