Potential Usefulness of PCA3 and EPCA-2 Tests for Early Detection of Prostate Cancer
I believe it is premature to comment on the potential usefulness of these new tests, PCA3 and EPCA-2, for early detection prostate cancer.
Both tests have been developed by good scientists. The PCA3 test is already available through certain clinical laboratories.
The basis of the PCA3 test is that it measures RNA from a gene that is over-expressed in many prostate cancers. In performing the test, a physician performs a rectal examination to massage fluid from the prostate gland into the urethra.
If the patient has prostate cancer, cancer cells will be present in the prostatic fluid. Then the patient is asked to urinate and the urine is tested for the amount of PCA3 RNA present in the cells. If cancer is present, there will be a considerable amount.
Thus, it is almost a way to diagnose cancer without the need to perform a biopsy, but not quite. A biopsy always has to be done to establish the diagnosis of cancer. One limitation of the PCA-3 test is that not all prostate cancers are in contact with the prostate gland’s ductal system and, therefore, may not appear in the urine. This situation would give a falsely negative result.
Another problem is that some men without cancer (at least cancer that can be easily diagnosed with a biopsy) can have high PCA3 levels.
Currently, PCA3 is most commonly used to determine which men who have an elevated PSA and a negative biopsy need to have a repeat biopsy. It is possible that genes other than PCA3 will become more useful than PCA3 in a similar diagnostic platform.
EPCA2 is a serum blood test that measures levels of a protein that occurs in the matrix of the nuclei of cells. It is not known what the protein is, how it works, or even why it is increased in the blood of men with prostate cancer.
Nevertheless, it appears to be elevated in many prostate cancer patients, and especially so in patients with more advanced-stagees of disease. Preliminary studies have suggested that it may be more accurate than PSA. Currently clinical trials are underway to test its accuracy.
I would like to see both PCA3 and EPCA-2 tested head-to-head with PSA and PSA derivatives and isoforms in an unselected group of men who present for prostate cancer screening to compare the relative usefulness of the tests.