Colon and Rectum Cancer Symptoms

This article describes the common symptoms that occur with cancer of the colon or rectum.  Colorectal cancer is a very common cancer.  It is the third most common cancer occurring in men and women in the United States.  It is also the third most common cause of cancer death as well, following lung and prostate cancers in men and lung and breast cancers in women.

Because colorectal cancer is so common, the emphasis on screening has been an important strategy from a public health standpoint.  It is currently recommended that everyone begins testing at the age of 50.  Certain people who are at a higher risk for colon cancer or have symptoms of it should begin sooner.

There are certain symptoms of colon cancer that occur early on and are vague and later symptoms that are more indicative of advanced disease.  This article will focus on the earlier symptoms because this represents the best chance for early diagnosis and cure.  The problem is that many of the earlier symptoms are not very specific and can occur from many other conditions that are not cancer.  Knowing what symptoms are important or “red flags” will assist you in getting proper screening sooner.

Symptoms of colon or rectal cancer include:

  • Blood in the stool (either bright red blood, old blood – often tarry or black, small amounts of blood only detectable with special testing)
  • Constipation
  • Abdominal Pain
  • Straining with bowel movements
  • Pain in the rectal area
  • Change in the bowel habits
  • Weight loss
  • Easy fatigue / lack of energy
  • Change in the caliber of stool
  • Diarrhea
  • Swelling of the abdomen
  • Nausea and vomiting

Of all of these symptoms, the most important symptom is finding blood in the stool.  Most people (including many physicians) will attribute blood in the stool to “hemorrhoids.”  This is a common error and even a fatal one if a colon cancer is missed.  Blood in the stool is never normal and should never be chalked up to “hemorrhoids” until it is properly evaluated by a physician.  A tumor growing in the colon will disrupt the lining of the colon and generally cause some amount of blood loss into the path of stool.

Blood can occur in many forms in the stool.  Red staining or bright red blood can be seen with every bowel movement or intermittently.  It may be seen on the stool or mixed within it.  Bright red blood in the stool is known as hematochezia.  It may only be noted at the end of the bowel movement with wiping (i.e. on the tissue paper).  The amount of blood is difficult to estimate as a few drops of blood will turn the water red and may appear larger than it is.  The character of the blood can vary based upon the volume of loss, rate of loss, and the source of the loss.  Bright red blood can be lost from the rectum or anal area or rarely from the upper intestine if it is bleeding rapidly.  Blood is a natural cathartic and stimulates the bowels to move faster.  Blood that has been stored in the intestines for many hours to days will turn a dark brown or black color and perhaps a tarry consistency.  This is known as melena.  Small amounts of blood may not be detectable to the eye and may not impart a red appearance to toilet bowl water.  The volume of blood may be small and not cause anemia or it may be significant and cause low blood counts with a pale appearance and lack of energy.  This is often how a colon cancer is suspected.  For example, a 65 year old otherwise healthy man has routine lab work checked at a physical exam and is found to have a hemoglobin count of 9 g/dL (normal about 15 g/dL).

Even if no blood is seen in the stool, microscopic amounts of blood can be detected by a quick and easy test that can be done in a physician’s office.  These tests are very accurate and if they detect blood this can prompt further evaluation.  The absence of blood does NOT mean there cannot be a colon cancer.  About 30% of people with colon cancer will not have blood detectable in the stool.  When blood is seen in the stool or detected in any form, the most accurate way to check for a colon cancer is to perform a colonoscopy.  This involves cleaning out the colon with laxatives and then passing a long snake-like camera from below to look throughout the colon for a tumor.  This usually involves sedation for comfort.  If a tumor is seen with the camera, a sample of the tumor can be taken with the camera to analyze for the presence of cancer.

Most other symptoms will fall under the category of “change in bowel habits.”  This is vague and can involve almost anything from constipation, more or less frequency, thin caliber stools, difficulty with passage of stools, etc.  As a colon or rectal cancer grows into the passageway, it can block the flow of stool either partially or entirely.  This creates a buildup and distention of the colon and intestines upstream to the blockage.  This is a common pattern seen with x-rays of the intestines that indicates a blockage (i.e. proximal distention, a transition point, distal decompression).

When a colon cancer has grown for some time, it will cause more severe symptoms such as pain, intestinal obstruction, spread to other areas such as the liver, weight loss, and fatigue.


  1. Townsend Jr, CM; Beauchamp RD; Evers BM; Mattox KL. (2008) Townsend: Sabiston Textbook of Surgery, 18thed.  Chapter 50.  New York, NY: Saunders.
  2. Goldman L, Schafer, AI;  (2011) Goldman: Goldman’s Cecil Medicine, 24th ed. Chapter 199. New York, NY: Elsevier
  5. This article was originally published on September 3, 2012 and last revision and update was 9/4/2015.