Repeated measures of the ratio of free to total prostate specific antigen (PSA) in a man's blood can predict a diagnosis of prostate cancer up to six years earlier than current prediction methods. This discovery by researchers at the National Institute on Aging (NIA) and colleagues at the Johns Hopkins University School of Medicine is published in the December, 1996, journal, Urology.

PSA, an enzyme produced by the prostate gland, is found in high concentration in semen where it acts to liquefy the seminal fluid after ejaculation so that sperm can swim freely. Some PSA leaks into the blood stream from prostatic cells, more so when the prostate enlarges. Part of the PSA binds to alpha-1 antichymotrypsin (ACT), a protein that prevents PSA from destroying cells by deactivating enzymatic function. Free PSA (the unbound form of PSA) is active in the semen, and becomes inactive when it spills into the blood. Free and bound PSA make up total PSA in serum.

Men whose total PSA levels are high may have prostate cancer or benign prostatic hypertrophy (BPH), an enlarged prostate gland. Earlier studies have found that the rate of increase in total PSA levels over several years is one of the best indicators of whether prostate cancer is present.

Currently, most physicians test for total PSA only, which, when measured repeatedly over time, can predict prostate cancer up to four years before clinical diagnosis," says Dr. James L. Fozard, Associate Scientific Director for the Baltimore Longitudinal Study on Aging (BLSA) at the National Institute on Aging (NIA), one of the study's authors. "This study, however, shows that measuring the ratio of free to total PSA repeatedly over time may lead to a prediction of prostate cancer up to 10 years before clinical diagnosis of prostate cancer.

The NIA and Hopkins team measured free and total PSA levels on stored, frozen sera from 26 men with no history of prostate disease (control), 29 men with BPH, and 23
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Contact: Suzanne Lewis
MillerM@31.nia.nih.gov
410-558-8114
NIH/National Institute on Aging
31-Dec-1996