Different Types of Colon Cancer Screening Tests
Screening Tests: Which Is Right for Me?
Colon cancer screening is the process of looking for signs of cancer or precancer in the colon and rectum before the patient notices any symptoms. When colorectal cancer is found in the early stages it is easier to treat and even curable. This is why the U.S. Preventive Services Task Force recommends regular colon cancer screening for all adults. You’re probably familiar with the colonoscopy exam, but there are actually several other methods available to screen for colorectal cancer.
Since screening tests are preventative measures used before symptoms are present, it’s important to remember that if you’re being offered a screening test, it’s not because your doctor thinks that you may have cancer — it’s because your age or health history place you into a group that may be at an elevated risk of developing cancer in the future. Colon cancer screening saves lives by identifying polyps before they’re able to develop into cancer or finding a colon cancer in the early stages where it can be cured or more easily treated.
What are the Types of Colon Cancer Screening Methods?
During a colonoscopy exam, your gastroenterologist observes the inside of the large intestine (colon) for specific signs of colon cancer, like polyps (abnormal growths that could turn into cancer). To do this, your doctor inserts a thin, flexible tube with a camera and a light attached on the end (called a colonoscope) into your rectum and throughout the colon. If your doctor finds polyps they are remove and sent to a lab for further testing. The results from these tests will determine whether the polyp is benign or cancerous.
Computed Tomography (CT) Colonography
CT colonography, also called virtual colonography, uses CT technology to produce multiple cross-sectional images of the intestinal tract. These images are combined on a computer to produce detailed images of the entire length of the colon. Your doctor uses these images to identify polyps or abnormal tissue that could be precancerous or cancerous. In order to capture small defects in wall, the colon is slightly inflated with air. This is done by inserting a small tube slightly into the rectum. This exam is strictly diagnostic and not therapeutic meaning it can find lesions such as polyps or cancers but cannot remove them. Any abnormal appearing lesions will require a colonoscopy exam for removal or tissue sampling.
Flexible sigmoidoscopy exams are essentially limited colonoscopies. The same equipment is used as with a colonoscopy but only the left side of the colon is examined. This exam is less invasive than a colonoscopy, carries fewer risk and usually can be done without sedation due to minimal discomfort. Just like a colonoscopy, polyp removal or biopsies can be done during the exam. Since this exam only looks at the more distal colon lesions in the rest of the colon will not be detected.
Stool tests involve testing a sample of feces for hidden blood in the stool. These test only detect the presence of blood and do not indicate what is bleeding or from what part of the intestine is bleeding. Since large polyps or colon cancers often bleed these test can be used to detect a possible problem. Stool tests are not intended to replace a regular colonoscopy, and if the results indicate the presence of blood your doctor will likely recommend a colonoscopy for further exploration.
Fecal Occult Blood Test (FOBT)
The fecal occult blood test is used to detect blood in the stool that cannot be seen by merely observing the sample. For an FOBT test, you’ll be asked to collect a stool sample at home. The sample is then tested in a lab using certain substances that detect blood by changing color. There are two types of fecal occult blood tests performed:
- Guaiac FOBT: Guaiac FOBT testing uses a chemical to detect a certain element of hemoglobin (a protein found in red blood cells), called heme. If you choose this test, you’ll be asked to follow a specific diet for a few days leading up to sample collection. This is because some foods contain heme and can skew results.
- Fecal immunochemical test (FIT): FIT testing uses specific proteins, called antibodies, that react to human hemoglobin in stool. No dietary restrictions are necessary for this test. It is much more accurate than the stool guaiac test as it will only detect the presence of human blood.
- Cologuard®: Cologuard® is a new screening method that combines a FIT test with a DNA laboratory test to detect existing colon cancer or advanced precancerous polyps (these are polyps that are actually turning into cancer). It is not indicated to detect most precancerous polyps. Cells from the lining of the large intestine are shed periodically and are passed through the stool. If there are cancerous polyps in the large intestine, cells from these polyps are also shed, and can be detected in the stool. Cologuard® looks for the DNA associated with colon cancer in these shed cells - as well as the presence of blood, which is an early sign of colon cancer - in the stool. Though Cologuard® can be a very beneficial test when ordered appropriately, it’s not right for all patients, particularly those who are already experiencing the symptoms of colon cancer. It is also not indicated in patients who have a history of precancerous polyps or a family history of colon cancer. If you’re interested in Cologuard®, it’s important to talk to your gastroenterologist about whether it’s the best option for you.
Misconceptions About Colon Cancer Screening Tests
Certain at-home tests, such as 23andMe, claim to be able to detect genetic variants associated with a higher risk of colorectal cancer. However, these tests are not considered a screening method and do not contribute to colorectal cancer prevention. This is because they merely detect inherited genes that may increase your risk of developing colon cancer. If you have inherited a gene that increases your risk of developing colorectal cancer, it does not mean that you will absolutely develop the disease. (And testing negative for a gene variant that increases colon cancer risk doesn’t mean that you won’t develop colon cancer.)
Genetic information should always be interpreted with a health professional in conjunction with your personal health history and your family health history. Having a family history of colon cancer does increase your risk but remember most people diagnosed with colon cancer do NOT have a family history.
The Bottom Line
The type of screening test recommended by your doctor will depend on your medical and family history. All of the available test have advantages and disadvantages including cost, accuracy and risk. Remember colon cancer is the second leading cause of cancer death in American and around 45,000 people will die from it this year alone. The only positive thing about this terrible disease is that in most cases it is actually preventable and curable simply by getting screened.
If the thought of getting a colonoscopy is keeping you from getting screened for colon cancer, ask your doctor about alternative screening options. Any screening is better than no screening. The most important thing is to get screened.