Colon Cancer Screening

Padma Ravichandran, Cancer Prevention and Treatment Fund

---

Colorectal Cancer (more commonly know as colon cancer) is cancer of the colon (large intestine) or rectum, both of which are part of the digestive system. The digestive system removes nutrients and minerals from the food we eat and beverages we drink, and uses them to help our body function. [1] The colon’s job is to remove water from the food that has been digested. The colon then passes the remains to the rectum, where they are eventually released from the body as fecal matter.[2]

In most cases, people with colon cancer don’t have any symptoms.[3]  However, possible symptoms of colon cancer include: blood in one’s stool, stomach aches and pains that do not go away, and weight loss that cannot be explained.  For information on how to prevent colon cancer, see “Colon Cancer: Who is at risk, and how can it be prevented?”

Screening for colon cancer is especially important because when colon cancer is found in the early stages, patients do very well: 9 out of 10 people will be alive five years after their diagnosis and treatment.[4] Colon cancer develops from polyps, or abnormal growths in the colon. Not all polyps become cancerous, but all colon cancers develop from polyps. You can get polyps at any age, but they are more common as you get older.[5] Colon cancer screening checks for these polyps, but it does not show whether the polyp is cancerous or precancerous. The only way to know is to remove the polyp and analyze it.

Screening Methods

There are several methods for colon cancer screening. For a quick look at the advantages and disadvantages of each method, see the chart at the end of this article

There has been a gradual increase in screening rates over the last ten years but even so, only about half of the U.S. population at highest risk gets screened for colon cancer. Studies show that people who don’t get screened are less likely to be insured and less likely to have a primary care physician.  In addition, it is widely known that screening for colon cancer is not fun.  And, some people believe that they do not need to get screened because they are healthy. It is not unusual for a person to get a positive test result (indicating polyps or something that is not normal), but not return for the follow-up test.

While there are various ways to screen for colon cancer, a colonoscopy is usually performed when any of the screening tests show abnormal results and follow-up is necessary. A flexible tube with a tiny camera is used to look inside the colon (the whole colon) and to remove any polyps found. Colonoscopy is used for both screening and treating  which is why it has become the most widely used screening method. It is important to know that a study published in the February 2012 issue of the New England Journal of Medicine found that colonoscopies are even more effective at preventing deaths from colon cancer than previously thought-reducing deaths by more than half.[6]

Researchers in the study found that patients who received colonoscopies and had noncancerous or pre-cancerous growths (polyps) removed, were much less likely to die from colon cancer than people in the general population. People in the general population may not have been screened for colon cancer or may have used different, less effective screening methods. The researchers, who followed most patients for almost 16 years but followed some people for as long as 23, concluded that there was a 53% reduction in the death rate from colon cancer in patients who had colonoscopies and then had polyps removed.⁶ While the study does not establish whether colonoscopies are better than other screening methods in reducing deaths from colon cancer, it brings welcome news.

The results of the NEJM study reinforce the importance of prevention. The United States Preventive Services Task Force (USPSTF) and the Center for Disease Control and Prevention (CDC) recommend that everyone get screened for colon cancer using FOBT, sigmoidoscopy, or colonoscopy starting at age 50 and continuing until age 75. They do not recommend the Stool DNA Test or Computed Tomography Colonography (“Virtual Colonoscopy”) because there is not enough evidence about the risks and benefits of each of these methods.[7]

USPSTF Recommended Screening Methods

Fecal Occult Blood Test (FOBT)

There are two types of FOBT: the Guaiac and Immunochemical tests. They are both take-home tests that detect the presence of blood in stool. The patient is asked to use a brush or Q-tip like tool to obtain a sample of stool. At the doctor’s office or lab they will run the tests and check for blood or the chemical units that make up blood.[8]

Doctors check for blood because it can indicate that a polyp in the colon or rectum broke and started to bleed.[9]

The guaiac-based fecal occult blood test (gFOBT) uses the chemical guaiac to test for heme.  Heme is part of the protein hemoglobin that is in blood, and it contains the iron that our body uses.[10] To make sure that this test is accurate, you will have to avoid certain foods starting two days before providing the stool sample. You should eat a diet high in fiber, but avoid red meats, vitamin C, and foods that might irritate your digestive system. Unfortunately, the results often inaccurately show that there is blood in the stool when there isn’t, which is why more testing is needed afterwards.

The immunochemical fecal occult blood test (iFOBT) uses antibodies to find blood in the stool. Research shows that the iFOBT is more accurate at detecting blood than the gFOBT and it does not require you to limit what you eat. The drawback, however, is that it is also more expensive. The iFOBT can cost anywhere from $18-$40, while the gFOBT costs a few dollars. Most insurance providers will pay for this test and it is also covered under Medicare once a year.[11]

The CDC recommends getting a FOBT every year.[12] If you have a positive FOBT, meaning there is blood in your stool, then your doctor may recommend that you get a follow-up colonoscopy to check for polyps.

Sigmoidoscopy

The sigmoidoscopy uses a lighted flexible tube (called a sigmoidoscope) with a tiny camera attached to examine the lower section of the colon and the rectum. The tube is inserted through the anus, up the rectum, and into the lower section of the colon. The procedure requires that the lowest part of the colon and rectum be clear of solids. In general, the doctor will prescribe a laxative and/or enema two hours before the procedure. The doctor may also ask the patient to restrict his or her diet to clear liquids for 1-3 days before the procedure.[13]

During the procedure, the doctor looks for inflamed tissue, abnormal growths and ulcers. Doctors can pass tools through the tube and remove any polyps or abnormal tissue. The growths can then be analyzed to determine if it is cancerous or not. Depending on the outcome of the test, the doctor may recommend getting a colonoscopy to check for polyps in the entire colon.

The sigmoidoscopy only lasts about twenty minutes, requires little preparation, and causes only mild discomfort. You may experience some cramping and bloating after the procedure but it usually only lasts about an hour. The drawback is that during the procedure there is a small chance of the colon or rectum tearing. Even though the procedure is less invasive than the colonoscopy, doctors are recommending the colonoscopy more often than the sigmoidoscopy.  Most doctors do not have the equipment for a sigmoidoscopy.  In addition the insurance reimbursement is less for the sigmoidoscopy than the colonoscopy.[14]

CDC recommends getting a sigmoidoscopy every five years. If the doctor finds polyps during the procedure he or she may recommend that you get a follow up colonoscopy.

Colonoscopy

 A colonoscopy is essentially a more comprehensive version of the sigmoidoscopy. The colonoscopy examines the entire colon and rectum using a longer lighted tube called a colonoscope. Similar to the sigmoidoscopy, the patients must clear their colon of solids before undergoing the procedure. The difference is that the colonoscopy requires that the entire colon be cleared, which requires more preparation. The doctor may tell you to go on a clear liquid diet 1-3 days before the procedure. In addition, your doctor will prescribe a laxative, and/or enema the night before the procedure. The laxative can be taken in pill or powder form. The powder form must be dissolved in water and is unpleasant. No matter the method of colon cleansing, the patient will need to use the bathroom several times, usually over several hours.

Because this procedure is so invasive, going even farther into the colon, you will be given anesthesia or some other sedative. Any time you are given anesthesia or medicine to make you less awake or sleepy, there is an added risk.[15] The colonoscope is inserted into the anus, up through the rectum, and into the colon. The doctor can check for inflamed tissue, ulcers, and abnormal growths and remove them if necessary. The removed tissue will then be analyzed to check if it is cancerous or not. The colonoscopy is usually recommended as a screening tool and a follow-up tool. This means that the procedure can be used to initially check for abnormal tissue, or it can be used when any of the other test results are positive for the presence of polyps.[16]

The procedures and recovery time for the colonoscopy is a little longer than the sigmoidoscopy. After the procedure, you will have to wait in the clinic for 1-2 hours until the sedative wears off. You will also need to make arrangements for someone to pick you up, because the doctor will not allow you to drive or take a taxi. As with the sigmoidoscopy, you may also experience cramping or bloating.

Due to how comprehensive and invasive the procedure is, the CDC recommends that you undergo a colonoscopy every 10 years. If they do find polyps during the procedure, they may ask you to repeat the procedure in less than 10 years.

Other Screening Methods

Stool DNA Test

The Stool DNA Test checks for any abnormal cells in the stool. For this test you need to collect an entire bowel movement, which may be unpleasant for some people, and send it in to the lab. There, they will look for certain DNA markers that indicate the presence of cancerous cells. Researchers have found that the Stool DNA Test is not very accurate or reliable. Its ability to detect colon cancer ranges from 20-71% so it is not cost effective to get this test.

Double Contrast Barium Enema (DCBE)

The DCBE uses x-rays and the metallic element Barium to examine the colon. They first clean out the colon and rectum using an enema that contains a solution with Barium. The Barium outlines the colon and rectum so it is more visible in the x-ray. There, doctors will be able to see any polyps or cancerous lesions.

The DCBE is effective at detecting certain growths, but often misses smaller polyps that may become cancerous. In most cases, the cancers that are found during the DCBE can also be found with a colonoscopy. Another concern is the amount of radiation you are exposed to during the procedure.  The DCBE has more exposure to radiation than the CT Colonography, which may lead to other adverse health problems.

Computed Tomography Colonography (CT Colonography)

CT Colonography-often called “Virtual Colonoscopy”-uses x-rays to create detailed visual images of the entire colon and rectum. However, in order to get good x-ray images, the colon and rectum must be cleared of solids by way of a clear liquid diet, enema, and/or laxative. As mentioned above, the laxative may be taken in pill or powder form. The powder form must be dissolved in water and is unpleasant. No matter the method of colon cleansing, the patient will need to use the bathroom several times, usually over several hours.

Once the x-ray images have been taken, a computer is used to assemble the pictures together to create a detailed picture of your colon and rectum. If the picture shows polyps or other abnormalities, a regular colonoscopy will be needed immediately to remove them.

Patients tend to prefer the CT Colonography because it is less invasive and causes less discomfort. This method is effective at identifying abnormal growths, but is not effective at identifying abnormal lesions that are flat or depressed. Another concern with the CT Colonography is exposure to radiation from the x-rays, which can increase your risk of getting cancer in the future even as it helps diagnose whether you have cancer currently.  Since the need to clear colon and rectum of solids with a laxative or enema is generally considered the worst part of a colonoscopy, the small advantages of the CT Colonography probably does not outweigh the decrease in accuracy and increase in radiation.

 

Procedure	Advantages	Disadvantages
FOBT	·  Preparation for the test is minimal ·  Sample can be collected at home ·  Very inexpensive	·  Getting “false-positive” results is common (you may be told you have a problem or something abnormal when you don’t). ·  Does not effectively detect all polyps and cancers ·  You must avoid certain foods for a  few days before collecting stool sample ·  Positive results may require additional tests, such as colonoscopy
Sigmoidoscopy	·  Quick procedure with minimal discomfort ·  Doctor can remove polyps during procedure ·  Only requires that the lowest part of the colon be clear	·  Does not examine the entire colon—only the lowest part of the colon and the rectum ·  Small risk of bleeding or tearing in colon ·  Positive results may require additional tests, such as colonoscopy
Colonoscopy	·  Doctor can view entire colon and rectum whereas sigmoidoscopy only looks at lower colon ·  Doctor can remove polyps during procedure ·  Is one of the most sensitive colon cancer screening tests available	·  May not find all polyps or growths ·  Preparation involves clearing entire colon through clear liquid diet and/or enema ·  Patient sedated during procedure ·  Procedure time varies depending on how many polyps are found ·  Patient must be picked up or driven home by someone else afterwards ·  Small risk of bleeding or tearing in colon
Stool DNA Test	·  Preparation for the test is minimal ·  Not invasive, so no risk of bleeding or tearing	·   Must provide entire bowel movement for testing ·  Not always accurate or reliable
Double Contrast Barium Enema	·  Doctor can view entire colon and rectum ·  Complications rare ·  No sedation necessary	·  May not find all polyps or growths ·  Preparation involves thorough cleansing of entire colon through clear liquid diet, enema, and/or laxatives ·  “False-positive” results possible ·  Doctor cannot remove polyps during procedure ·  Positive results may require colonoscopy or other additional procedures
CT Colonography    “Virtual  Colonoscopy”	·  Doctor can view entire colon and rectum ·  Not invasive, so no risk of bleeding or tearing	·  May not find all polyps or growths ·  Preparation involves thorough cleansing of entire colon through clear liquid diet, enema, and/or laxatives ·  You will be exposed to some radiation (see “Everything You Ever Wanted to Know About Cancer and Radiation but Were Afraid to Ask”) ·  Positive results will require follow-up colonoscopy; recommended immediately after virtual procedure to avoid a second appointment and to biopsy lesions quickly

 

References:

1. National Cancer Institute. Colorectal cancer PDQ: General information about colorectal cancer. 2009.   Retrieved 22 Feb 2010 from the National Cancer Institute Web Site:  http://www.cancer.gov/cancertopics/pdq/screening/colorectal/Patient/page2
2. National Institute of Health and National Library of Medicine. 2008. Large intestine. Retrieved on 24 Feb 2010 from the  MedLine Web Site: http://www.nlm.nih.gov/medlineplus/ency/imagepages/19220.htm
3. Center for Disease Control and Prevention. 2009. Colorectal cancer: Screening saves lives. Retrieved on 23 Feb 2010 from the Center for Disease Control and Prevention Web Site:  http://www.cdc.gov/cancer/colorectal/pdf/SFL_brochure.pdf
4. Center for Disease Control and Prevention. Colorectal cancer screening rates. 2010. Retrieved on 24 Feb 2010 from the Center for Disease Control and Prevention Web Site: http://www.cdc.gov/cancer/colorectal/statistics/screening_rates.htm
5. National Cancer Institute. Dictionary of cancer terms: Adenoma. 2009. Retrieved on 24 Feb 2010 from the National Cancer Institute Web Site:  http://www.cancer.gov/dictionary/?CdrID=46217
6. Zauber AG, Winawer SJ, O’Brien M.J, Lansdorp-Vogelaar I, van Ballegooijen M, Hankey BF, et al.  Colonoscopic polypectomy and long-term prevention of colorectal-cancer deaths.  New  England Journal of Medicine.2012; 366(8), 687-696.
7. United States Preventive Services Task Force. Screening for colorectal cancer. 2008. Retrieved on 18 Feb 2010 from the Agency for Healthcare Research and Quality Web Site:  http://www.ahrq.gov/clinic/uspstf/uspscolo.htm
8. Center for Disease Control and Prevention. Colorectal cancer screening basic fact sheet. 2009. Retrieved on 23 Feb 2010 from the Center for Disease Control and Prevention Web Site:  http://www.cdc.gov/cancer/colorectal/pdf/Basic_FS_Eng_Color.pdf
9. Chen, JH and Lin, HH. Colorectal cancer screening. Tzu Chi Medical Journal. 2009; 21 (3), 190-196.
10. National Cancer Institute. Colorectal cancer screening. 2009. Retrieved on 18 Feb 2010 from the National Cancer Institute Web Site:  http://www.cancer.gov/cancertopics/factsheet/Detection/colorectal-screening
11. Levi, Z, Rozen, P, Hazazi, R.  A quantitative immunochemical fecal occult blood test for colorectal neoplasia. Annotated Internal Medicine. 2007; 146, 244-255.
12. Center for Disease Control and Prevention.Colorectal cancer screening tests. 2010. Retrieved on 22 Feb 2010 from the Center for Disease Control and Prevention Web Site: http://www.cdc.gov/cancer/colorectal/basic_info/screening/tests.htm
13. National Institute of Health. Flexible sigmoidoscopy. 2008. Retrieved on 24 Feb 2010 from the National Digestive Diseases Information Clearinghouse Web Site: http://digestive.niddk.nih.gov/ddiseases/pubs/sigmoidoscopy/
14. Klabunde, CN, Lanier, D, Nadel, M, McLeod, C, Yuan, G, Vernon, SW. Colorectal cancer screening by primary care physicians: Recommendations and practices 2006-2007. American Journal of Preventive Medicine. 2009; 37 (1), 8-16.
15. National Institute of Health. Colonoscopy. 2010. Retrieved on 24 Feb 2010 from the National Digestive Diseases Information Clearinghouse Web Site: http://digestive.niddk.nih.gov/ddiseases/pubs/colonoscopy/
16. Neri, E, Faggioni, L, Cerri, F, Turini, F, Angeli, S, Cini L, Perrone, F, Paolicchi, F, Bartolozze, C.  CT colonography versus double-contrast barium enema for screening of colorectal cancer: comparison of radiation burden. Abdominal Imaging. 2009.