Is an improved PSA screening test in sight?

A fter decades of searching for a replacement for prostate-specific antigen (PSA) in prostate cancer screening, many researchers are once again examining variations on the long-beleaguered biomarker. PSA has withstood years of skepticism from critics who blame it for the overdiag-nosis and overtreatment of millions of men since it became the favorite prostate cancer screening test in the early 1990s. But PSA is staying put in the clinic. Now, instead of focusing on new markers of prostate cancer , many researchers are looking for ways to enhance PSA's predictive powers. " PSA has been very effective in changing the landscape of prostate cancer, but it still has a number of signifi cant limitations that need to be addressed, " said Robert Getzenberg, Ph.D., director of research at Johns Hopkins University's urological institute. PSA was fi rst identifi ed in 1966 and quickly proved useful for identifying semen in criminal cases of sexual assault. Further studies in the 1980s suggested its utility as a prostate cancer screening tool, but physicians were skeptical of a test with such low sensitivity and specifi city. Prostate cancer causes elevated PSA levels, but so do benign conditions like prostate enlargement or infl ammation. Even though PSA wasn't a marker of cancer, it was associated with the risk of cancer. In 1994, the U.S. Food and Drug Administration approved PSA screening for the early detection of prostate cancer. Today PSA remains controversial and is being tested in large randomized screening trials. One such trial, the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial, is trying to determine whether screening tests like PSA reduce cancer deaths. But results of the trial won't be available for several years. In the meantime, the PSA test will probably remain the primary screening test. " For prostate cancer, it's still our good old PSA, " said Sudhir Srivastava , Ph.D., chief of the cancer biomarkers research group at the National Cancer Institute. " There are some candidate biomarkers for prostate cancer, but nothing really compares to PSA at this point in time. All the data we know of are very preliminary and need to be validated. " Researchers have been looking for a new prostate cancer biomarker throughout PSA's screening career. There has been no shortage of promising rising stars, but none has withstood the test of time and validation. " The problem isn't with coming up with biomarker X, …