College of American Pathologists
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  Colorectal Cancer


Updated July 31, 2009

What is colorectal cancer?
Colorectal cancer occurs when cells lining the colon or rectum become abnormal and divide uncontrollably. Cancer cells can invade and destroy healthy tissue. These cells can spread to form new tumors in other parts of the body.

Colorectal cancer screening tests save lives. Fortunately, survival rates are as high as 90 percent if the disease is diagnosed and treated in its earliest stages–but less than 40 percent of colorectal cancers are discovered at that stage. Despite the wide availability of several types of colorectal cancer screening tests, only about half of screen eligible people in the United States have been screened.

The American Cancer Society’s most recent estimates for colorectal cancer in the United States are for 2009:

  • 106,100 new cases of colon cancer
  • 40,870 new cases of rectal cancer
  • 49,920 deaths from colorectal cancer1

Colorectal cancer can be prevented and treated with early detection and removal of pre-cancerous polyps before they develop into cancer. Pre-cancerous polyps may be present in the colon and rectum for years before invasive cancer develops, which provides several opportunities for screening tests to successfully identify them so that they can be removed.

What is a colorectal cancer screening test?
These screening tests include laboratory type, non-invasive tests that either identify blood in the stool, known as fecal occult blood tests (FOBT) or that identify DNA shed from colorectal cancer and polyps in the stool, known as stool DNA tests (sDNA). These tests are primarily used for early detection of cancers themselves, which leads to early treatment.

The most common colorectal cancer screening test currently is the fecal occult blood test (FOBT). To be most effective, it should be performed on three separate stool samples each year and be repeated each and every year. The FOBT can be performed at home by the patient and the test cards returned to the physician of laboratory for analysis. Some FOBT’s can be performed and read by a person himself or herself at home. Stool DNA testing requires only a single stool specimen, which can then be sent to a specialized laboratory for analysis.

More invasive tests, where a clinician can actually see the colon lining, include flexible sigmoidoscopy (FS) and colonoscopy. FS uses a shorter instrument which only looks at the left side of the colon, an area where about half of colorectal cancers arise. Because FS doesn’t view the entire colon, it is generally used in combination with annual fecal occult blood testing. Colonoscopy uses a longer instrument (colonoscope), and allows the clinician to view entire colon. Colonoscopy is generally performed with intravenous sedation or anesthesis in some cases.

Finally, there are also less invasive X-ray based approaches. These include double contrast barium enema, which is rarely used, and a new approach, CT colography, which uses Computerized Axial Tomography (“CAT Scan”) and special software, which create a virtual image of the colonic lining for review.

The invasive and X-ray techniques are more sensitive to finding colonic polyps than FOBT. While more expensive and labor intensive for both the patient and clinician, these tests are better able to detect and remove polyps as well as identify cancer at its earliest stages.

All positive colorectal cancer screening tests, except for colonoscopy itself, need to be confirmed by a subsequent diagnostic colonoscopy.

What should I expect at my colorectal cancer screening test?
The best test is the one that you will actually use as directed. All screening tests are superior to not being screened at all. Discuss which test is right for you with your clinician and make certain to get screened, because colorectal cancer can be prevented and successfully treated when identified early.

There are several tests used to screen for colorectal cancer. Your physician may recommend one or a combination of tests from the list below, depending on your risk factors and health history. Screening tests for colorectal cancer include:

Fecal occult blood test (FOBT)
The fecal occult blood test (FOBT) is a simple test done at home. The test checks for hidden (occult) blood in the stool. Test kits are available at pharmacies, or your physician may order a testing kit for you to use at home. The FOBT is a first-line test because cancerous tissue and precancerous polyps are more likely to bleed than normal colorectal tissue, and the test detects this bleeding. A yearly FOBT increases the chances that any bleeding will be detected. In fact, people between 50 and 80 years old who have an FOBT every year are 33 percent less likely to die of colorectal cancer than are their peers who do not have regular FOBTs.

Preparing for and taking the FOBT
The test is performed on three different bowel movements. Bleeding, when it occurs, is often unpredictable and intermittent. It is very important to check three separate stools to increase the chance that if bleeding is present, it will be found. In order to get the 33 percent survival advantage that FOBT has been shown to provide, it is very important that three separate stools are checked each year. To improve the effectiveness of the test, avoid certain foods that can cause a false positive result for at least two or three days before your first test, and continue to avoid these foods until you have collected all three samples.


  • turnips, radishes, and horseradish
  • red meats
  • iron supplements
  • aspirin, products that contain aspirin and anti-inflammatory medications
  • vitamin C supplements

Eat plenty of:

  • vegetables, especially lettuce, spinach, and corn
  • fruits, particularly apples, prunes and grapes
  • cereals and breads with bran

Some of the newest more sensitive FOBT tests may require that only two stools are sampled. Newer FOBT’s are also not effected by diet. Discuss with your physician whether the FOBT he or she recommends is of this type.

Do not perform the test during your menstrual period or if you have bleeding caused by hemorrhoids. Do not test a stool sample if it has come into contact with toilet bowl water that has turned blue from cleaning products.

When you are ready to take the test, follow the directions provided with the test kit. Don’t skip steps.

Taking the FOBT

  1. The most common FOBT home kits use stool cards (these cards will show a color change if blood is detected in your stool). Follow the same process for each of the three bowel movements you test.
  2. Complete any necessary identification information on the front of each slide. When you have a bowel movement, collect a small amount of stool on one end of the applicator. To catch the stool, your kit may have paper to place over the toilet seat and above the water. If not, use plastic wrap or a container. If you use a container, clean and rinse it before use to avoid affecting the test results.
  3. Apply a thin smear of stool inside the box (usually box A) marked on the slide.
  4. Use the applicator to get a second sample from a different part of the stool. Apply a thin smear of the second sample inside the other box (usually box B) marked on the slide.
  5. Close the cover of the slide.
  6. If your kit has developer solution, wait three to five minutes (or as specified in the kit instructions) before applying one drop of the developer solution to the area with the stool samples. Apply one drop of the developer solution to the control areas of the card so that you will be able to tell what positive and negative test results should look like. Read the results within 10 seconds. (For these timed steps, use a stopwatch or a watch with a second hand. Don’t guess at the time.)
  7. If your kit does not have developer solution, return all of the slides (from all three bowel movements) to your doctor in person or by mail within four days of collecting the samples.
  8. Remember to do this for three different bowel movements.
  9. If you find blood in your stool, call your doctor as soon as possible.

Test results
Depending on the test kit you are using, you may not be able to see the test results yourself. If your kit was given to you by your physician, you may have to return the test cards to your doctor, who will send them to a medical laboratory to determine the results.

A normal test means that there was no detectable blood at the time you collected your stool samples. If your test kit does show results, a normal test will be indicated by no color change—it will be negative for the presence of blood in your stool.

Keep in mind that a negative test does not completely rule out the possibility of colorectal cancer or polyps. That’s why it’s important to have an FOBT every year.

An abnormal test, which will show a color change, is considered positive for the presence of blood in your stool.

If you get a positive test result, it is possible that it may be due to something other than colorectal cancer or polyps. The FOBT has a high rate of false-positive results, meaning that the test result will be abnormal even if the person does not have colorectal cancer or polyps. Depending on your age and other risk factors for colorectal cancer, your doctor may ask you to repeat the FOBT or move ahead with additional testing (colorectal endoscopy, barium enema, or flexible sigmoidoscopy.)

Stool DNA Testing (sDNA)
The stool DNA test identifies mutated and altered DNA that is being shed by colorectal cancers and pre-cancerous polyps into the stool stream. This DNA is released from cells that shed from the polyps and cancers as they grow. Polyps and cancers are directly caused by changes in DNA, as opposed to simple bleeding, which is not directly related to the cause of the cancer but which can occur when cancers or polyps ulcerate. Most cancers and polyps are caused by the acquisition of these DNA changes as people get older. There are some specific inherited DNA changes that are associated with very high likelihoods and early onset development of colorectal cancer, but these are relatively uncommon. Most colorectal cancers and polyps develop as a result of acquired DNA changes.

The sDNA test must be ordered by a clinician and requires a single stool sample that can be collected at home with a collection kit provide by the laboratory. The collection system fits on the toilet bowl so that the stool sample is easily passed into a small bucket. Then, a buffer solution, provided in the kit, is poured over the stool and bucket is sealed. The top of the bucket is then labeled with the person’s name and the date and time that the stool was passed. It should be brought or sent to the laboratory within 24 hours. No direct contact or manipulation of the stool sample is needed.

The laboratory isolates the human DNA from the stool sample and evaluates it for mutations and alteration known to be associated with colorectal cancer. If the test is abnormal, a person is referred for colonoscopy for further evaluation.

Just like with FOBT, the sDNA test will not find all the cancers or polyps (false negative) and if the test is positive, it does not mean that a colon cancer or polyp will definitely be found on colonoscopy (false positive). Colorectal cancer generally develops slowly over a number of years and regular screening over many years increases the chance that colorectal cancer will be found at an early stage and treated successfully.

Digital rectal examination (DRE)
A digital rectal examination (DRE) involves a physician inserting a gloved finger into the rectum to feel for any bumps or abnormal areas. DRE is not an acceptable form of colorectal cancer screening by itself. Even when done with an in-office FOBT, DRE is not accurate enough as it will miss about 95 percent of cancers. An effective FOBT must be performed on multiple stool samples as described above.

Flexible sigmoidoscopy
Flexible sigmoidoscopy is a procedure in which your physician examines the rectum and lower colorectal with a lighted instrument called a sigmoidoscope, a flexible tube about 60 cm long and about as thick as a finger.

Preparing for flexible sigmoidoscopy
Because your rectum and lower colorectal must be completely clean of stool, your doctor will give you detailed information about cleansing your bowel. This will help make the procedure briefer and more accurate.

Be sure to inform your physician about any medications you are taking and any allergies you have. Certain drugs, such as aspirin, increase the risk of bleeding, and your doctor may ask you to stop taking certain medications for several days before you have the procedure.

Taking the test
Flexible sigmoidoscopy rarely causes significant discomfort. You may experience feelings of bloating, pressure or cramping at various stages of the procedure. You will probably lie on your left side while the tube is inserted and moved into your rectum and lower colorectal. Your physician may use visual control or watch an image generated on a TV monitor. The procedure, which lets your doctor make a careful examination of the entire lining of your rectum and lower colorectal, will usually take less than 15 minutes.

Test results
If your doctor finds an area in the colorectal that needs additional evaluation, he or she will obtain a small sample of the tissue (called a biopsy) and send it to the pathology laboratory for examination. The pathologist will look at the sample under a microscope to find any abnormal cells.

If your physician finds any polyps, he or she may obtain biopsy samples for further study. Polyps, which are small growths on the inner lining of the colorectal and rectum, are usually benign (not cancerous). Some, however, are pre-cancerous. If your polyps are found to be pre-cancerous, your physician will most likely ask you to have a colorectal endoscopy.

Colonoscopy, like flexible sigmoidoscopy, is a procedure wherein your physician examines your colorectal by inserting a flexible tube and a lighted instrument into your anus, rectum and through the colorectal. The colorectaloscope is longer than a sigmoidoscope. The physician may use a TV monitor to monitor the tube’s progress. Your doctor may recommend that you have regular colorectaloscopies if you have a previous history or a family history of polyps or colorectal cancer.

Preparing for colonoscopy
Your physician will give you detailed information about completely cleansing your colon. This may involve taking a special solution or following a strict diet of clear liquids for several days or using laxatives or enemas before the test.

Let your doctor know about any medications, prescription or non-prescription, that you are taking. Certain drugs increase the risk of bleeding, and other drugs (such as arthritis medications, iron preparations, and insulin) may require special instructions. Tell your doctor about any allergies you have, too.

Taking the test
Before the procedure begins, you will be given an IV and a monitor for your heart, blood pressure, and blood oxygen levels. You may be given medication through the IV to make you sleepy and relaxed.

During the procedure, you may have feelings of bloating, pressure and cramping, but the medication will help you relax so that you will not feel any significant pain.

Test results
If your doctor finds a polyp in your colon or rectum, he or she may remove it and send it to the pathology laboratory for microscopic examination. If your doctor finds anything else abnormal, he or she may perform a biopsy (take a sample of tissue) and send it to the pathology laboratory for examination.

By examining a polyp or biopsy, a pathologist can determine whether you have cancer or a pre-cancerous abnormality. Your tissue may also appear abnormal due to inflammation.

Barium enema with air contrast
The barium enema with air contrast (or double contrast barium enema), uses barium and x-ray tests to help define the anatomy of the rectum and colorectal. Barium sulphate is placed into the rectum through the anus to partially fill and open up the colorectal. Once the colorectal is about half full, the patient is turned on an x-ray table to spread the barium throughout the colorectal. Air is then inserted, which causes the colorectal to expand, and good x-rays can be taken.

Preparing for the barium enema with air contrast
Before undergoing the test, you must eliminate as much fecal material as possible from your colorectal and rectum. Your physician will provide instructions about following a clear liquid diet and using any cleansing enemas.

Women who are or may be pregnant should alert their physicians.

Taking the test
Because your colorectal and rectum will be filled with barium, a white liquid, you will probably feel some fullness or mild discomfort in your abdomen. An x-ray machine will be placed in front of you, and film will be behind you.

The procedure itself may last from 15 minutes to an hour, depending on the problem being evaluated and your anatomy. Any air added with the barium will further define the structures of the bowel.

Test results
A radiologist will look at the x-rays to see if there are any abnormalities present in the colorectal.

Why should I be screened for colorectal cancer?
Colorectal cancer can be prevented by removing precancerous polyps, which may be revealed through screening tests years before invasive cancer develops. Frequently, there are no symptoms, so regular screening is the only way to tell.

Survival rates are high when colorectal cancer is discovered early at a localized stage, and only about 10 percent of patients will die from it within five years. If the disease is detected as it begins spreading within the colon, but before it has affected other organs, about 35 percent of patients will die within five years. If the disease is diagnosed at an advanced stage (spreading beyond the colon to distant sites), death rates are high—over 90 percent of patients will die within five years.

The College of American Pathologists and other medical professional organizations recommend regular screening for colorectal cancer beginning at age 50. Screening starting at age 45 was recently recommended for African Americans. Individuals with a family history of either colorectal cancer or polyps may need to be screened earlier and more often, and should discuss an appropriate screening schedule it with their physicians.

Who is at risk for colorectal cancer?
The risk of developing colorectal cancer generally increases as people get older. Men and women 50 years and older are at higher risk for developing colorectal cancer. African-Americans are more likely than Caucasians to be diagnosed with colorectal cancer at a more advanced stage and are more likely to die from it. That is why screening starting at age 45 has been recommended for African Americans.

Aside from age, other risk factors for colorectal cancer include having:

  • inflammatory bowel disease
  • a family history of colorectal cancer or colorectal polyps
  • certain hereditary syndromes (such as familial adenomatous polyposis [FAP] or hereditary non-polyposis colorectal cancer [HNPCC, also known as Lynch syndrome])

Which tests should be done?
There are several screening options for early detection of colorectal cancer. Beginning at age 50, men and women should follow one of these options:

  • FOBT every year
  • Stool DNA (sDNA) testing, interval not determined
  • Flexible sigmoidoscopy every five years
  • Double contrast barium enema every five years
  • CT Colography every five years
  • Colorectaloscopy every 10 years starting at age 50
  • Note: Flexible sigmoidoscopy can be combined with a yearly FOBT. All positive tests should be followed up with a colorectaloscopy. Work with your physician to outline the best plan for you.
  • Individuals at a moderate or high risk should talk with their doctors about different screening schedules.

The College of American Pathologists offers two patient information websites to help remind Americans to receive a colorectal exam, as well as understand the disease.
Sign up to receive a free e-mail message reminding you to have your colorectal cancer screening tests at

Visitors to the site select the day they would like to schedule their colorectal cancer screening. On the chosen date, an e-mail will be sent reminding the patient to call their primary care physician or other health care provider and schedule an appointment.
If you or a loved one has been diagnosed with colorectal cancer, the College of American Pathologists offers free, accurate information about colorectal cancer to patients through

Visitors to can find answers to their questions about colorectal cancer; available treatment options; questions they should ask their doctors; a glossary of key terms, as well as pictures of normal and diseased cells.


  1. American Cancer Society - May 2009