Fecal (stool) tests are used to detect colon cancer. Only very small stool samples are needed for these non-invasive cancer tests. There are several different methods currently in use.
They include:
- Fecal Occult Blood Tests (FOBT)
- Fecal DNAAbbreviation for deoxyribonucleic acid. Composed of very long strings of nucleotides, which are abbreviated as A, C, G and T. DNA is the storage form of our genetic material. All of the instructions for the production of proteins are encoded in our DNA. Test
Fecal Occult Blood Test (FOBT)
Fecal occult blood tests (FOBT) are able to detect small hidden (occult) blood present in stools, a possible sign of colon cancer or colonic polyps (precursors of cancer). Occult blood refers to very small amounts of blood that cannot be seen by visual inspection, but can be detected using chemical tests. The detection of blood in stool does not necessarily indicate cancer, it simply helps health care professionals make an accurate diagnosis. There are currently two methods used to detect occult blood, they are described below.
Guaiac Fecal Occult Blood Test (GFOBT)
The GFOBT detects the activity of peroxidase, an enzymeA protein that speeds up the process of chemical reactions in the body without becoming altered in the process. Almost every biological process is driven by the activity of enzymes. Without enzyme catalysts, the complex reactions that build and break down cell parts would not happen at a rate compatible with life. Enzyme names usually describe the reaction that is being catalyzed and all of them end in -ase. found in the blood. The test can be done using a home kit obtained from a health care provider. It requires a sample taken of the inside and the outside of three separate bowel movements. The samples are then placed on appropriate slides and returned for testing. Some foods, medications, and supplements can cause false positives, so be sure to carefully follow instructions from your health care provider or the test manufacturer.1, 2
Fecal Immunochemical Test (FIT)
The fecal immunochemical test is a more advanced, easier to use FOBT that has shown a better combination of sensitivity and specificity. The test uses antibodiesAntibodies are proteins produced by a type of white blood cell (B cells or B lymphocytes). Antibodies are able to stick very tightly to specific targets. Antibodies are currently being used as anti-cancer drugs (i.e. Herceptin). to detect the presence of blood hemoglobin. This method is not affected by food, medication, or supplements and it is also easier for subjects to obtain an adequate sample. The FIT only requires samples from the surface of two bowel movements. Although the FIT is more user friendly, it is still important to carefully follow your health care providers instructions.1, 2
Colon cancer often forms as extensions to the colon wall. These growths can be hit by passing food and cause cancer cells and blood to be released into the colon. The cells and blood leave the body with the stool (feces).
Samples of stool can be examined for the presence of blood cells. If blood is found, it could indicate that colon or rectal cancer.
Fecal DNA Test
As part of the normal turnover that occurs in the cells that line the bowel, many of the epithelialA type of tissue (epithelium) that covers our exposed surfaces, such as skin. Also lines our hollow or tube-like organs/tissues such as the digestive tract. Since these tissues are often exposed to environmental insults such as chemicals and solar radiation and are often divide rapidly to replace lost cells, many cancers arise in epithelial tissues. cells that line the intestines are shed into the waste. As discussed in the section on tumor suppressors, many colon cancers share a common genetic defect in the APC geneA stretch of DNA that leads to the production of an RNA. The RNA is produced during the process of transcription. This RNA can be used to guide the formation of a protein via translation or can be used directly in the cell.. The cells that are shed into the fecal matter contain DNA and tests have been developed to detect mutations in the APC gene. This technique is able to detect the DNA from colon cancer cells even at early stages of cancer. Its non-invasive nature makes it a promising new screening tool.3, 4
In 2014, the FDA approved the first stool DNA test for colon cancer, Cologuard®.5, 6, 7 The test detects mutations in genes associated with colorectal cancer, and modifications (methylation) of other cancer genes. The test also detects the presence of hemoglobin (blood) in stool. Like any medical test, Cologuard® is not 100% accurate. In a large clinical trial, the test was able to detect 92% of stage 1-4 colorectal cancers.8 Because the genetic changes seen in cancer happen over time, the test can also detect pre-cancerous conditions. In the clinical trial, the test was able to detect 69% of 'high risk' pre-cancers, those thought to be most likely to progress to cancer.8
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