What is colorectal cancer?

Cancer that begins in the colon is called a colon cancer, while cancer in the rectum is known as a rectal cancer. Cancers affecting either of these organs also may be referred to as a colorectal cancer. Colorectal cancers generally develop over time from adenomatous (precancerous) polyps — growths — after a series of mutations (abnormalities) arise in their cellular DNA. The exact cause of colorectal cancer is not known. Some of the risk factors for colorectal cancer involve a family history of colon or rectal cancer, diet, alcohol intake, smoking, and inflammatory bowel disease.

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What parts of the body are affected by colorectal cancer?

To understand colorectal cancer, it is helpful to understand what parts of the body are affected and how they work.

The colon

The colon is an approximately 5 to 6-foot long tube that connects the small intestine to the rectum. The colon — which, along with the rectum, is called the large intestine — is a highly specialized organ that is responsible for processing and storing waste. The colon periodically empties its contents — stool — into the rectum to begin the process of elimination.

The rectum

The rectum is a 5- to 6-inch chamber that connects the colon to the anus. It is the job of the rectum to hold the stool until defecation (evacuation) occurs.

What are the signs and symptoms of colorectal cancer?

Unfortunately, some colorectal cancers might be present without any signs or symptoms. For this reason, it is very important to have regular colorectal screenings (examinations) to detect problems early. The best screening evaluation is a colonoscopy. Other screening modalities include fecal occult blood tests, flexible sigmoidoscopy, barium enema, and CT colonography (virtual colonoscopy). The age at which such screening tests begin depends upon your risk factors, especially a family history of colon and rectal cancers.

However, most colorectal cancers are associated with signs or symptoms. One of the early signs of colorectal cancer is bleeding. However, tumors often bleed only small amounts, off and on, so that evidence of the blood is found only during chemical testing of the stool, which is called a fecal occult blood test. Other signs and symptoms include:

  • Change in bowel habits: Constipation, diarrhea, narrowing of stools, incomplete evacuation, and bowel incontinence — although usually symptoms of other, less serious problems — can also be symptoms of colorectal cancer.
  • Blood on or in the stool: By far the most noticeable of all the signs, blood on or in the stool can be associated with colorectal cancer. However, it does not necessarily indicate cancer, since numerous other problems can cause bleeding in the digestive tract, including hemorrhoids, anal tears (fissures), ulcerative colitis, and Crohn's disease, to name only a few. In addition, iron and some foods, such as beets, can give the stool a black or red appearance, falsely indicating blood in the stool. However, if you notice blood in or on your stool, see your doctor to rule out a serious condition and to ensure that proper treatment is received.
  • Unexplained anemia: Anemia is a shortage of red blood cells, the sort that carry oxygen throughout the body. If you are anemic, you may experience shortness of breath. You may also feel tired and sluggish, so much so that rest does not make you feel better.
  • Abdominal pain or bloating
  • Unexplained weight loss
  • Vomiting

If you experience any of these signs or symptoms, it is important to see your doctor for evaluation. For a patient with colorectal cancer, early diagnosis and treatment can be life-saving.

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