Biomarkers for Colorectal Cancer
What are biomarkers?
Biomarkers are molecules that indicate the presence of disease or some of its characteristics. Diagnostic tests measure biomarkers in blood or tissue specimens. Biomarkers can be any type of molecule, but most of the existing cancer diagnostic tests in blood (e.g., PSA for prostate cancer) measure proteins.
We already know that colonoscopy can detect colorectal cancers early—so why develop a blood test for colorectal cancer?
Only about half of people who should get colonoscopies (recommended every 10 years, beginning at age 50) actually get the test. Although colonoscopy is very safe, there is a small risk of damage to the colon. Some people are put off by the invasive nature of the procedure and by the bowel prep, which uses strong laxatives to clear the colon for the exam. Evidence of cancer, precancer or small polyps is detected in less than 20% of people who have colonoscopies. The purpose of a blood test for early stage colorectal cancer is to more efficiently identify those with colon cancer biomarkers in their blood. A positive test would lead to a followup colonoscopy.
A blood test for cancer—how would it work?
The theory behind a blood test for cancer is that cells in the growing cancer will release some proteins into the blood. Such proteins could serve as biomarkers detected by a blood test. Certain cancers do release protein molecules into the blood (e.g, PSA from prostate cancers, CA125 from ovarian cancers and thyroglobulin from thyroid cancers). However, none of these markers detect early stage cancers very well. We suspect that other proteins or combinations of several proteins in the blood could provide more sensitive, accurate indication of early stage cancers. To develop an effective test, we must identify one or more proteins that appear in the blood when cancers are developing.
How will the Ayers Institute identify biomarkers for early stage colorectal cancers?
The Ayers Institute has begun a program to collect colon tissue from people who undergo colonoscopies or colon cancer surgery. We have collected samples of colon cancers, precancers, polyps and normal tissues and analyzed their proteins to determine which are most highly characteristic of cancers. We have identified several dozen biomarker “candidates”, which are present at much higher levels in the cancers. These candidates are being evaluated to identify which are measurable in blood and are present at higher levels in people with colorectal cancers and precancers. Biomarker candidates most strongly associated with cancer will be evaluated further as components of a new test for early stage cancers.