A new form of the prostate-specific antigen (PSA) test is now available to screen for prostate cancer, the second leading cause of cancer death among men in this country. Called complexed PSA or cPSA, the test measures the level of PSA that has been complexed or bound with alpha-1-antichymotrypsin in a patient's blood sample.

Some organizations are touting cPSA as a more accurate form of PSA blood testing for the detection of early stage prostate cancer. The Prostate Cancer Education Council, which sponsors Prostate Cancer Awareness Week, decided to offer the cPSA test during this year's screening events in hopes of evaluating its performance compared to standard PSA tests.

PSA exists in three major forms in the blood: 1) free, 2) bound to a protein called alpha-1-antichymotrypsin, and 3) bound to another protein called alpha-2 macroglobulin. People with prostate cancer have more of the form bound to alpha-1-antichymotrypsin and less of the free form than do healthy men or those with benign diseases of the prostate.

Initial screening for prostate cancer commonly uses the total PSA test, which measures all but the third form of PSA. If the result is slightly elevated, follow-up testing is often performed using another test that measures free PSA. These tests have been criticized by some as being associated with too many false positives and false negatives. It was hoped that the new cPSA test would replace these so that only a single screening test would be needed.

In one large, multi-center study that included researchers from Johns Hopkins and the New York University School of Medicine, the cPSA test demonstrated improved specificity over a total PSA assay, reducing the number of false positives and leading the investigators to conclude that cPSA could be used as a first-line test for prostate cancer screening. However, in several studies published this year, the advantage of cPSA over total and free PSA tests was less convincing. In one trial at the University of Texas M.D. Anderson Cancer Center, the cPSA assay was found to only be equivalent to a total PSA test for early detection. In another study of 535 patients conducted by McGill University, the ratio of free-to-total PSA performed better than either cPSA or total PSA alone in prostate cancer detection.

Until this issue becomes clearer through additional studies, it is important to understand that a cPSA test is available but also that there are advantages as well as drawbacks to each of the various approaches to PSA testing, including cPSA tests. Men should discuss all of their PSA test results with their doctor.