REVIEW – July – August 2008

The possibilities of laboratory tests for colorectal cancer screening


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The article gives an overview of laboratory tests for colorectal cancer (CRC) screening. In March 2008 American oncologists, radiologists and gastroenterologists issued the first-ever joint consensus guidelines for CRC screening. According to the experts´ recommendations, annual guaiac-based fecal occult blood test (FOBT) with high test sensitivity for cancer, annual fecal immunochemical FOBT with high test sensitivity for cancer and stool DNA test with high sensitivity for cancer with an uncertain testing interval were considered acceptable options for early detection of CRC.
FOBT is the most common screening test. Large randomized clinical trials have shown that screening with serial FOBT causes reduction in the incidence of CRC and reduces CRC mortality.
For detection of fecal occult blood, two common methods are used: the guaiac-based method and the immunochemical method. The disadvantages of guaiac-based testing are  the need for dietary restrictions before sample collection and limited sensitivity of single application. However, it is the only test proved to be effective in reducing CRC mortality and incidence. Immunochemical test only reacts with human globin and requires no dietary restriction. As globin is degraded by the enzymes of the upper GI tract, it detects bleeding from the lower parts of the bowel.
Stool DNA is a novel test in the screening panel. Carcinoma cells that contain altered DNA are continuously shed into the large bowel lumen and DNA itself is quite stable in stool. It can already be detected in the preclinical stage of illness. The test is noninvasive, requires only a single stool collection and has acceptable sensitivity for CRC. The limitations of testing are high cost, optimal choice of DNA mutations and insufficient data of the testing interval.
As CRC screening evidently reduces mortality and incidence, there is good reason to start screening in Estonia.