Colon Cancer (Colorectal Cancer)

  • Medical Author:
    Francis W. Nugent, MD

    Dr. F.W. Nugent is a medical oncologist specializing in gastrointestinal cancers with a special interest in pancreatic cancer. Dr. Nugent graduated from Middlebury College with a bachelors degree in religion before graduating from Albany Medical College. He presently serves as vice-chairman of medical oncology at the Lahey Clinic in Burlington, Massachusetts.

  • Medical Editor: Jay W. Marks, MD
    Jay W. Marks, MD

    Jay W. Marks, MD

    Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.

Quick GuideColon Cancer: Symptoms, Signs, Screening, Stages

Colon Cancer: Symptoms, Signs, Screening, Stages

Is it possible to prevent colon cancer?

The most effective prevention for colorectal cancer is early detection and removal of precancerous colorectal polyps before they turn cancerous. Even in cases where cancer has already developed, early detection still significantly improves the chances of a cure by surgically removing the cancer before the disease spreads to other organs.

Regular physical activity is associated with lower risk of colon cancer. Aspirin use also appears to lower the risk of colon cancer. The use of combined estrogen and progestin in hormone replacement therapy lowers the risk of colon cancer in postmenopausal women. Hormone replacement therapy has risks which must be weighed against this effect, and should be discussed with a doctor.

Digital rectal examination and stool occult blood testing

It is recommended that all individuals over the age of 40 have yearly digital examinations of the rectum and their stool tested for hidden or "occult" blood. During digital examination of the rectum, the doctor inserts a gloved finger into the rectum to feel for abnormal growths. Stool samples can be obtained to test for occult blood (see below). In men, the prostate gland can be examined at the same time for evidence of prostate cancer.

An important medical screening test for colorectal cancers and polyps is the stool occult blood test. Tumors of the colon and rectum tend to bleed slowly into the stool. The small amount of blood mixed into the stool usually is not visible to the naked eye. The commonly used stool occult blood tests rely on chemical color conversions to detect microscopic amounts of blood. These tests are both convenient and inexpensive. A small amount of stool is smeared on a special card for occult blood testing. Usually, three consecutive stool cards are collected. A person who tests positive for stool occult blood has a 30% to 45% chance of having a colon polyp and a 3% to 5% chance of having a colon cancer. Colon cancers found under these circumstances tend to be small and not to have spread and have a better long-term prognosis.

It is important to remember that having stool tested positive for occult blood does not necessarily mean a person has colon cancer. Many other conditions can cause occult blood in the stool. However, patients with a positive stool occult blood test should undergo further evaluations involving barium enema X-rays, colonoscopies, and other tests to exclude colon cancer and to explain the source of the bleeding. It is also important to realize that stool which has tested negative for occult blood does not mean that colorectal cancer or polyps do not exist. Even under ideal testing conditions, at significant percentage of colon cancers can be missed by stool occult blood screening. Many patients with colon polyps do not have positive stool occult blood. In patients suspected of having colon tumors and in those at higher risk for developing colorectal polyps and cancer, screening flexible sigmoidoscopies or colonoscopies are performed even if the stool occult blood tests are negative.

Recent developments in stool testing have led to both the FIT ( fecal immunohistochemical test) for occult blood, and perhaps more exciting, the Cologuard test for both blood, and DNA analysis. The former test appears more sensitive than the old stool “guiac” tests. The latter is both more sensitive and specific. It is appropriate for screening in normal risk patients over 50 to about 75 years of age as a screening for both larger polyps and colon cancers. It does not replace the need to scope testing to be discussed below.

Screening: Flexible sigmoidoscopy and colonoscopy

The term "screening" is properly applied only to the use of testing to look for evidence of cancer or pre-cancerous polyps in individuals who are asymptomatic and at only average risk for a type of cancer. Those patients who, for example, have a positive family history of colon cancer, or are symptomatic for a colon abnormality, undergo diagnostic testing rather than screening tests.

Screening can involve evaluation of the colon by the same tests discussed earlier; barium enema, flexible sigmoidoscopy, or colonoscopy. Beginning at age 50, a flexible sigmoidoscopy, plus a barium enema screening test is recommended every 3 to 5 years. Flexible sigmoidoscopy is an exam of the rectum and the lower colon (60 cm or about two feet in from the outside) using a viewing tube (a short version of colonoscopy). Recent studies have shown that the use of screening flexible sigmoidoscopy can reduce mortality from colon cancer. This is a result of the detection of polyps or early cancers in people with no symptoms. If a polyp or cancer is found, a complete colonoscopy is recommended. The majority of colon polyps can be completely removed at the time of colonoscopy without surgery. Recommendations now are that screening colonoscopies instead of screening flexible sigmoidoscopies should be done for healthy individuals starting at ages 50 to 55. Please read the Colon Cancer Screening article.

Colonoscopy uses a long ( 120 to 150 cm)  flexible tube which can examine the entire length of the colon. Through this tube the doctor can both view and take pictures of the entire colon, and also can take biopsies of colon masses and remove polyps.

Patients with a high risk of developing colorectal cancer may undergo screening colonoscopies starting at earlier ages than 50. For example, patients with family history of colon cancer are recommended to start screening colonoscopies at an age 10 years before the earliest colon cancer diagnosed in a first-degree relative or 5 years earlier than the earliest precancerous colon polyp discovered in a first-degree relative. Patients with hereditary colon cancer syndromes such as FAP, AFAP, HNPCC, and MYH are recommended to begin colonoscopies early. The recommendations differ depending on the genetic defect. For example, in FAP colonoscopies may begin during teenage years to look for the development of colon polyps. Patients with a prior history of polyps or colon cancer may also undergo colonoscopies to exclude recurrence. Patients with a long history (greater than 10 years) of chronic ulcerative colitis have an increased risk of colon cancer, and should have regular colonoscopies to look for precancerous changes in the colon lining.

Genetic counseling and testing

Blood tests are now available to test for FAP, AFAP, MYH, and HNPCC hereditary colon cancer syndromes. Families with multiple members having colon cancers, multiple colon polyps, cancers at young ages, and other cancers such as cancers of the ureters, uterus, duodenum, and more, should be referred for genetic counseling, followed possibly by genetic testing. Genetic testing without prior counseling is discouraged because of the extensive family education that is involved and the complicated nature of interpreting the test results.

The advantages of genetic counseling followed by genetic testing include: (1) identifying family members at high risk of developing colon cancer to begin colonoscopies early; (2) identifying high-risk members so that screening may begin to prevent other cancers such as ultrasound tests for uterine cancer, urine examinations for ureter cancer, and upper endoscopies for stomach and duodenal cancers; and (3) alleviating concern for members who test negative for the hereditary genetic defects.

Diet and colon cancer to prevent colon cancer

People can change their eating habits by reducing fat intake and increasing fiber (roughage) in their diet. Major sources of fat are meat, eggs, dairy products, salad dressings, and oils used in cooking. Fiber is the insoluble, nondigestible part of plant material present in fruits, vegetables, and whole-grain breads and cereals. It is postulated that high fiber in the diet leads to the creation of bulky stools which can rid the intestines of potential carcinogens. In addition, fiber leads to the more rapid transit of fecal material through the intestine, thus allowing less time for a potential carcinogen to react with the intestinal lining. For additional information, please read the Colon Cancer Prevention article.

Medically reviewed by Jay B. Zatzkin, MD; American Board of Internal Medicine with subspecialty in Medical Oncology


Greene, Frederick L. et al., eds. AJCC Cancer Staging Manual. 6th ed. New York, NY: Springer, 2002.

Medically Reviewed by a Doctor on 2/23/2016

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