Researchers are developing more screening tests for prostate cancer. Like the PSA test, they rely on biomarkers, such as antigens or proteins, which are elevated or may only be present in men who have prostate cancer. The hope is that these newer tests will better detect existing cancers (better sensitivity), and will not raise the alarm for cancer when it is not present (better specificity).
Prostate-specific membrane antigen (PSMA). This substance is found in all prostate cells. PSMA levels are higher in men with prostate cancer, but also increase as men get older. The PSMA blood test has been found to be highly sensitive, but as a screening tool, the PSMA has not proved superior to the PSA test. The PSMA test is currently used as part of an imaging scan to determine whether prostate cancer has spread to other areas of the body. It has also shown promise as a predictor of recurrent prostate cancer.
Early prostate cancer antigen (EPCA-2). This test is for a protein that is present in the nucleus of cancerous cells. Small amounts of EPCA-2 leak into the bloodstream, so EPCA-2 can be measured with a blood test. In April 2007, a study in the journal Urology reported that the EPCA-2 test is highly sensitive for prostate cancer. What’s more, the test was able to accurately distinguish between cancer that was confined to the prostate and cancer that had spread beyond the prostate. On the downside, eight of the 35 men in the study with BPH (but no cancer) were identified as having elevated levels of EPCA-2, suggesting that false positives may be a problem. Over all, the data were preliminary, but promising. The EPCA-2 test is still in clinical trials and is not yet available to the public.
Autoantibodies. Sometimes the amounts of proteins produced in cancerous cells are too small to measure in a blood test. But these proteins can function as antigens, triggering the body’s immune system to produce relatively large amounts of antibodies that can be measured in blood samples. Antibodies that attack the body’s own proteins are called autoantibodies. Researchers at Harvard and the University of Michigan have identified an autoantibody signature (essentially a fingerprint) of autoantibodies produced against prostate cancer proteins. The autoantibody signature test holds great promise, but the research is still in the very early stages.
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