The neglected sex gland: a protein in the blood forecasts cancer of the prostate

Science News, August 8, 1992 by Kathy A. Fackelmann

Nonetheless, men have the best chance of finding prostate cancer early if they allow doctors not only to take blood for a PSA reading, but also to do the rectal exam, which sometimes finds very small tumors that won't markedly elevate PSA readings, Catalona adds.

"The most complete evaluation of the prostate gland is when you use both PSA and the rectal exam:' agrees PSA researcher Joseph E. Oesterling of the Mayo Clinic in Rochester, Minn. "That allows you to detect the greatest number of prostate cancers."

What is PSA anyway? Like cholesterol, which the body manufactures to help keep cell membranes strong, PSA serves a much-needed function in the healthy man. The protein is manufactured by the epithelial cells that line the prostate gland. When a man ejaculates, his semen is initially very thick. To help the sperm swim to their destination, PSA liquefies the semen.

While young men have a low concentration of PSA in their bloodstream, that concentration tends to rise as they age. Scientists believe the increase occurs because the prostate expands as a man gets older. More prostate cells simply mean more PSA in the blood, explains Jay D. Pearson of the National Institute on Aging's Gerontology Research Center in Baltimore.

If PSA concentrations in the blood simply reflected the size of a man's prostate, however, oncologists wouldn't be able to home in on cancers. Researchers also know that malignant tumors secrete far more PSA than would be expected based on volume alone. Pearson and H. Ballentine Carter of the Johns Hopkins University School of Medicine in Baltimore and their colleagues used that knowledge to devise another method of investigating prostate tumors ! The team relied on the Baltimore Longitudinal Study of Aging, a long-term project funded by the National Institute on Aging. Participants in the study, which began in 1958, undergo several days of medical tests every two years. For their particular project, the researchers searched study records to find 20 men who had developed benign prostatic hyperplasia and 18 who had received the bad news of prostate cancer at some point during their participation. For purposes of comparison, they also identified 16 men with no sign of prostate trouble. All of the men had participated in the aging study for at least seven years.

Next, the researchers analyzed each volunteer's blood samples, which had been frozen and stored at two-year intervals. The investigators wanted to get a picture of how PSA changes over time, especially among men eventually stricken with prostate cancer.

Their findings proved intriguing: Five to 10 years before a diagnosis of prostate cancer, PSA concentration in the blood starts to rise rapidly and exponentially. In men who eventually developed BPH, PSA also increased, but at a much slower rate. The team detailed their findings in the April 22/29 JOURNAL OF THE AMERICAN MEDICAL ASSOCIATION.

By tracking the rate of change, the researchers could differentiate between men who would eventually develop BPH and those who would suffer prostate cancer. About 40 percent of men with BPH will have a PSA blood level of 4 micro-grams per liter or higher. Right now, doctors often err on the side of caution and recommend that such men get a biopsy to look for malignant cells.