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

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

Tucked away under the bladder in a man's body is the walnut-size prostate gland that often labors away under a cloak of anonymity Many men don't know they have this male sex gland. Others don't know where the prostate is located or what it does. And when something goes wrong with the prostate, even doctors can't always tell whether the condition is a life-threatening cancer or a relatively harmless enlargement.

For much of a man's life, the prostate gland produces some of the fluid, or semen, that carries sperm through the urethra during sexual climax. But after age 50, the prostate can begin causing trouble.

For reasons not well understood, the prostate gland often gets larger as a man ages. Indeed, more than half of all men in their 60s suffer from an enlarged prostate, a condition called benign prostatic hyperplasia (BPH). If the gland gets too big, it can squeeze the urethra, the tube that also carries urine from the bladder. This pressure can cause a weakened or hesitant urine stream or an increased need to urinate, especially at night.

While the symptoms of BPH can be annoying, a second, more serious threat involving the prostate gland plagues older men: cancer. Men with BPH are not at increased risk for prostate cancer; however, symptoms of prostate cancer and BPH are often identical. Even worse, doctors don't have a foolproof diagnostic test to distinguish between BPH and cancer of the prostate, a disease that will kill an estimated 34,000 men in the United States in 1992 alone.

Until recently, doctors looking for prostate cancer had to rely on a test known as the digital rectal exam. After pulling on gloves, the physician inserts a finger into the rectum and probes for any hard lumps that may indicate the presence of cancer. While this time-honored test does reveal some malignancies, it misses a large number of prostate tumors. Furthermore, the rectal exam often turns up only advanced cancers - those that have spread beyond the prostate wall and thus are more deadly

Within the last few years, a protein known as prostate-specific antigert (PSA) has taken center stage in the fight against this potentially lethal cancer. For some time after PSA's discovery more than 20 years ago, the molecule attracted little attention. Then, during the 1980s, a slew of researchers began to take another look at PSA. The scientific community's renewed interest in PSA accelerated about a year ago, when William J. Catalona of the Washington University School of Medicine in St. Louis and his colleagues published a pioneering report on PSA and prostate cancer.

By measuring the concentration of PSA in the bloodstream, Catalona's team found they could detect more prostate cancers than they could by relying on the rectal exam alone.

"We found that PSA was the most powerful test we had:' Catalona says about the study, reported in the April 25, 1991 NEw ENGLAND JOURNAL OF MEDiCiNE. The findings fueled a virtual boom in PSA blood tests ordered by doctors around the country,

More than a year later, most scientists would agree that, although a powerful predictor of prostate cancer, PSA has shortcomings. Still, "PSA may be better than anything we have, even though it's not perfect," Catalona says. His group and several other research teams are now searching for ways to refine PSA's ability to flag prostate cancer and distinguish it from a harmlessly enlarged prostate.

The key to curing prostate cancer is finding the malignancy very early in the disease process - well before the cancer spreads. Catalona's team now has evidence that the PSA blood test can detect prostate cancer before it travels to the bone or other body sites. That finding sparks the hope that early detection will lead to longer lives for men afflicted with this disease, Cata1ona told SCIENCE NEWS.

His team began their study by looking at a group of 274 men being evaluated for possible prostate cancer. All had gone to their doctor prior to 1991 and had received the traditional rectal exam, which discovered suspicious lumps in the prostate. A biopsy, in which a physician takes a needle and withdraws a small number of cells from the suspect tissue, showed that 36 of the 274 men had cancer of the prostate. Furthermore, 24 of the 36 (67 percent) had advanced cancer at the time of their diagnosis. Because doctors had to rely on the rectal exam, most of the cancers they detected had already metastasized. Such cancer is much harder to cure because it has spread beyond the prostate, Catalona notes. To see if they could detect prostate cancer before it runs amok, the team began to use the PSA blood test as a screening test for outwardly healthy men. They recruited more than 10,000 men age 50 and over. None had reported trouble with his prostate prior to entering the study, These recruits all had an initial PSA blood test, followed by a biopsy if their PSA values were at least 4 micrograms per liter of blood -- concentrations that can indicate a malignancy That initial screening identified 244 men with prostate cancer. However, just 86 (35 percent) of those men had prostate cancer that had spread at the time of their diagnosis. Men who passed the initial PSA test came back for additional blood tests later in the study The team discovered another 46 men with prostate cancer during this process, but just 13 of them (29 percent) had advanced cancer. Taken together, these results indicate that widespread PSA screening could stop many prostate cancers before they can kill, Catalona says. He presented his group's data in May at the American Urological Association meeting in Washington, D.C. Nearly 70 percent of prostate cancers discovered by means of a rectal exam have already reached a potentially deadly stage. PSA screening reverses that lethal trend, enabling doctors to find cancers still confined to the prostate gland. At that stage, surgeons can remove the diseased gland or radiologists can kill the cancerous tissue with radiation therapy In most cases, such therapy can cure prostate cancer. Anticancer drugs are not as effective. Men appear more willing to have their blood drawn for a PSA test than to undergo a rectal exam, Catalona notes. While most men are used to getting their blood tested for cholesterol and other markers of disease, they often balk when doctors suggest an uncomfortable rectal exam, he says.