Newer screening tests

Researchers are developing more screening tests for prostate cancer. Like the PSA test, they rely on biomarkers such as antigens or proteins that are elevated or may be present only in men with prostate cancer. The hope is that these newer tests will be better at detecting existing cancers (better sensitivity) and will not raise an 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 with age. The PSMA blood test has been shown to be highly sensitive, but as a screening tool, the PSMA has not been shown to be 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 cancer cells. Small amounts of EPCA-2 enter the bloodstream, so EPCA-2 can be measured with a blood test. In April 2007 a study in the journalurologyreported that the EPCA-2 test is highly sensitive for prostate cancer. In addition, 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 other hand, eight of the 35 men in the study with BPH (but no cancer) were found to have elevated EPCA-2 levels, suggesting that false positives could be a problem. Overall, the data was 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 protein produced in cancer cells are too small to measure in a blood test. But these proteins can act as antigens, causing 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 is promising, but the research is still in its infancy.