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Colon Cancer Screening
by Douglas K. Rex, MD
Douglas K. Rex, MD is Chancellor's Professor and Professor of Medicine at Indiana University School of Medicine and Director of Endoscopy
at Indiana University Hospital in Indianapolis. He graduated from Harvard College, Summa Cum Laude and with highest distinction from
Indiana University School of Medicine. He received the Outstanding Teacher Award in the Introduction to Medicine course five times and
has been awarded the Indiana University School of Medicine Outstanding Teacher Award as well as and Department of Medicine's Excellence in
Teaching Award. He is a full-time clinical gastroenterologist at Indiana University Hospital. His major research interests have been in
colorectal disease and, in particular, colorectal cancer screening and the technical performance of colonoscopy. He co-authored the colorectal
cancer screening recommendations of the American College of Gastroenterology and those of the Gastroenterology Consortium. He has served as
the ACG representative to the National Colorectal Cancer Round Table, and from 2000-2006 was the chairman of the U.S. Multi-Society
(ACG, ASGE, AGA, ACP-ASIM) Task Force on Colorectal Cancer. He has also served in the American College of Gastroenterology as Chairman of the
Board of Governors, Secretary, and Treasurer and is a Past President of the ACG.
Table of Contents
Introduction
In the United States, colorectal cancer (which is sometimes simply called "colon cancer") is the second leading cause of death from cancer and third most
common cancer diagnosed in men and women1. The good news is that, if diagnosed while still confined to the colon, the five–year survival rate
for patients with colon cancer is 90%. Early detection is critical, since the survival rate drops to 68% if the cancer has spread to the lymph nodes
and to 10% if the cancer has metastasized to other parts of the body. Although there is no question that early detection is critical, less than
half of Americans aged 50 or older undergo routine screening2.
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What is colon cancer?
Healthy cells grow and divide to form new cells as your body needs them. Cancerous cells reproduce when your body does not need them, forming a mass of
cells called a tumor, which can be benign or malignant. In colon cancer, tumors typically arise from the cells that line the colon (also known as
the large intestine) and/or the rectum.
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Who is at risk for colon cancer?
Colon cancer is most common in people aged 50 years or older. Most colon cancers begin in colorectal polyps (growths that protrude from the inner wall
of the colon and/or rectum). The following photos show a normal colon and a colon with a polyp. Polyps are benign, but can be considered pre–cancerous,
especially those determined by a pathologist to be adenomas. Finally, if you have inflammatory bowel disease (IBD) and/or a family history
of colon cancer, you are also at increased risk. (For more information about IBD and colon cancer, refer to the IBD and Cancer newsletter.)
This photo shows the lining of a normal colon.
This photo shows a colon with a polyp.
Keep in mind that lifestyle (for example, smoking, obesity, and lack of exercise) plays an important role in which at–risk individuals actually develop
colon cancer. However, about 80% of all colon cancer cases occur in people with no family history of colon cancer and without IBD3.
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How is colon cancer detected?
In the early stages of colon cancer, some people may experience changes in bowel habits; blood in stool; unexplained weight loss, fatigue, or stomach pain;
and/or bloating and cramps. However, others may have no warning symptoms. Screening tests can help your doctor find and remove polyps or cancer
before symptoms occur. This is critical, since the treatment of colon cancer is more likely to be effective if the disease is found early. Adults
without risk factors should have their first colon cancer screening at age 50, and adults with risk factors should undergo more frequent screening
beginning at an earlier age.
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What screening tests are available?
There are two general types of colon cancer screening tests: fecal tests and partial or full structural exams. Fecal tests are used to identify colon
cancer and may also detect some premalignant adenomatous polyps. They include the guaiac fecal occult blood test (gFOBT), the fecal immunochemical
test (FIT), and the stool DNA (sDNA) test. Partial or full structural exams are used to detect both cancer and premalignant adenomatous polyps. They
include colonoscopy, sigmoidoscopy, double contrast barium enema, and computerized tomographic (CT) colonography (also called virtual colonoscopy).
Fecal tests
gFOTB
Sometimes colon cancer or polyps may bleed, and the gFOBT can detect very small amounts of blood in the stool. The Hemoccult SENSA is the most sensitive
of the gFOBTs and is the only type recommended. If blood is detected, follow–up colonoscopy is required to identify the source of the blood,
since benign conditions like hemorrhoids can also cause blood in the stool.
The gFOBT can be done at home and requires taking two samples from each of three consecutive bowel movements. For each sample, a small amount of stool
is placed on a special card provided by a doctor and then the card is returned to the doctor or a lab. Some foods, drugs, and vitamins can increase
the risk of false positives or negatives. For example, you must not consume red meat, poultry, fish, some raw vegetables, or vitamin C for three days prior to the test, and you must not consume aspirin or nonsteroidal anti–inflammatory drugs (NSAIDs) for seven days prior to the test. The
gFOBT should be repeated annually.
FIT
Like the gFOBT, the FIT can detect very small amounts of blood in the stool. Other similarities are that the FIT should be repeated annually, and a positive
FIT must be followed by colonoscopy. However, unlike the gFOBT, no dietary restrictions are required prior to the FIT, and some types of FIT
require fewer stool samples and/or less direct handling of stool.
sDNA
The sDNA test can detect some, but not all, cells from adenomas or tumors that are shed into the intestinal space and passed in the stool. It is a new
screening method, so the technology is still evolving. A benefit of the sDNA test, when compared to the gFOBT or FIT, is that it is not dependent on blood detection, which may be intermittent and nonspecific. The sDNA test also requires only a single (but larger) stool sample, which must be packaged
in a customized collection kit and shipped with a special ice pack that must be placed in the freezer at least eight hours prior to use. Like
the other fecal tests, a positive sDNA test must be followed by a colonoscopy. Because the sDNA test is relatively new, the appropriate screening interval has not been determined.
Partial/full structural exams
Colonoscopy
Colonoscopy is one of the most commonly performed medical procedures in the United States, and it is also the most comprehensive and reliable screening
method for colon cancer. During the procedure, the inside of the rectum and entire colon are examined using a long, thin, flexible tube (a colonoscope)
connected to a camera and a video display monitor. If polyps or tumors are found, they are removed and tested. Colonoscopies generally take from 15 minutes to an hour to complete and are relatively safe and pain free. You may choose to take a mild sedative prior to the procedure, in which
case you must arrange for a family member or friend to drive you home from the clinic. If your colonoscopy is normal and you have no other risk factors,
you should repeat the procedure every ten years.
Before a colonoscopy, your colon must be emptied of all stool, so that its entire length can be easily examined. The first step is to consume only liquids
on the day before your procedure. The second step is to use a bowel preparation product that causes diarrhea, so that all solid waste is eliminated
from the digestive tract. Be sure to follow your doctor's instructions, which will vary depending on the type of preparation prescribed, the time of day your colonoscopy is scheduled, and your medical history. There are several bowel preparation options, including:
- Sodium phosphate tablets – a series of virtually tasteless tablets, taken with any clear liquid
- Sodium phosphate solution – two to three glasses of salt solution plus additional liquid
- Polyethylene glycol (PEG) lavage – either two or four liters of nonabsorbable liquid, sometimes used in conjunction with laxatives and additional
liquids
Bowel preparation can cause dehydration, since you will lose fluids quickly, so it is important to stay hydrated before, during, and after using a bowel
preparation product. Be sure to drink at least the amount of fluid specified with your prescription.
Sigmoidoscopy
During a sigmoidoscopy, the inside of the rectum and the lower part of the colon are examined using a sigmoidoscope, which is similar to a colonoscope,
but does not examine the upper part of the colon. As with a colonoscopy, if polyps or tumors are found, they are removed and tested. A follow–up
colonoscopy is required if sigmoidoscopy detects adenomas.
Sigmoidoscopy is typically performed without sedation and should be repeated every five to ten years. The bowel preparation typically consists of two enemas, but better preparation is achieved using sodium phosphate tablets, PEG lavage, or sodium phosphate solution.
Double–Contrast Barium Enema
When a barium solution (which looks and feels like watery chalk) is put into the colon and rectum using an enema (a tube inserted into the rectum) and then air is pumped in through a flexible catheter, a detailed outline of the colon and rectum can be seen in an x–ray. Multiple x–rays are
taken to examine different angles of the colon.
Preparation for a double–contrast barium enema involves a 24–hour dietary and laxative regimen, which must be thorough or the test will not
be accurate. The barium enema is typically administered without sedation and should be repeated every five years. If one or more polyps larger than
5 mm are detected, a follow–up colonoscopy is required.
Virtual colonoscopy
Virtual colonoscopy, which is also called "computerized tomographic (CT) colonography," uses a CT scan to produce two– and three–dimensional
images of the entire length of the colon. Preparation for the procedure, which takes about ten minutes and does not require sedation, is similar to preparation for a colonoscopy. Then, a thin tube is inserted into the rectum and air is pumped through the tube to inflate the colon to facilitate
viewing. If one or more polyps larger than 5 mm are detected, a follow–up colonoscopy is required. Virtual colonoscopy should be repeated every
five years.
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Does health insurance cover screening?
Because there is currently no federal legislation requiring insurance companies to pay for preventive screening, coverage varies and you must check with
your insurance provider to determine your benefits.
Medicare recipients are entitled to colonoscopy screenings every ten years, sigmoidoscopy and double–contrast barium enema screenings every five years, and annual fecal occult blood tests, whereas Medicaid coverage varies by state.
The Colorectal Cancer Legislation Report Card is an annual assessment of each state's preventive screening legislation. It is supported by a coalition
that includes the American Cancer Society Cancer Action Network, American College of Gastroenterology, American Gastroenterological Association, American
Society of Colon and Rectal Surgeons, American Society of Gastrointestinal Endoscopy, and many other organizations. According to the 2008 report,
more than half of the U.S. population benefits from state laws requiring insurance providers to cover cost of colon cancer screening tests, but
26 states still do not assure screening coverage. If that is the case in your state, urge your elected officials to support such legislation.
Free or low–cost screening is available in a number of areas, including the following locations:
Suffolk County, NY (631–444–7644)
Baltimore, MD (410–887–3456 or 1–866–632–6566)
King, Clallam, and Jefferson counties, WA (1–800–756–5437)
Nebraska (1–800–532–2227)
St. Louis, MO (314–879–6392)
To locate free or low–cost screening elsewhere in United States, call 1–800–4–CANCER or 1–800–ACS–2345.
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Questions to ask your doctor
When you meet with your physician to discuss colon cancer screening, it may help to have a list of questions to help guide the discussion. The following
are some suggestions to help you get started.
- Which test do you recommend?
- What preparation is necessary?
- How sensitive is the test?
- How often is there a false positive test?
- What are the risks involved?
- Does the test help prevent colon cancer by finding precancerous polyps, or is it primarily a test that will detect early cancer?
- How much does the test cost?
- Will my insurance cover any of the cost?
- How long will the test take and how long will it take to get results?
- In what instances will additional testing be necessary?
Click here to print out and take to your doctor.
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Conclusion
According to the Centers for Disease Control, four out of every ten people who should be screened for colon cancer are not being tested within the suggested
timeframe4. Remember that colon cancer screening gives you the power to stop colon cancer before it starts. More than half of all instances of
colon cancer could be prevented if everyone age 50 and older was screened regularly5. If you are at least 50 years old or have any of the risk factors
described in this newsletter, call your physician and schedule an appointment.
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