Prostate screen: blood test rates best.

Prostate screen: Blood test rates best

Men with prostate cancer face some grim statistics. About 30,000 die from this disease in the United States each year, in part because 70 percent of all cases go undertected until the malignancy has spread beyond the prostate gland.

A simple blood test -- already used in prostate cancer patients to track their response to chemotherapy -- now offers the best hope yet for early diagnosis, report William J. Catalona and his co-workers at Washington University School of Medicine in St. Louis.

Physicians today diagnose prostate cancer in a two-step process that involves checking for an enlarged prostate gland -- traditionally by palpating the gland from inside the rectum -- and then analyzing prostate cells removed from patients found to have an enlarged gland. Not only do many men avoid the uncomfortable rectal exam; the manual probing is also a very subjective procedure whose usefulness depends on the skill of the physician.

Catalona's group tried another approach: measuring blood levels of prostate-specific antigen (PSA), a protein produced exclusively by the prostate gland and present at elevated levels in men with prostate cancer and other prostate diseases. In the April 25 NEW ENGLAND JOURNAL OF MEDICINE, the researchers describe a study of more than 1,600 men aged 50 and older. The PSA test, they report, correctly identified 30 percent more prostate cancer cases than did rectal exams and uncovered 40 percent more cases than did an ultra-sound scope, a new device used by some urologists to examine the gland visually. The authors have since screened more than 7,000 additional men, and the percentages reported in the paper "have help up really well," Catalona told SCIENCE NEWS.

His team also reports that the blood test yielded fewer false-positives than either of the other two screening methods, meaning that fewer men with high PSA levels turned out not to have cancer when their prostate cells were biopsied. The lowest error rate emerged from a combination of the PSA screen and traditional rectal exam.

"The rectal exam [alone] is not really as accurate as physicians thought it was," Catalona says. Pairing rectal examination with the PSA screen "has the potential to dramatically improve the detection of prostate cancer."

Scientists don't know yet whether earlier detection would improve survival rates for prostate cancer patients as it does forwomen with breast cancer, cautions Martin I. Resnick of University Hospitals of Cleveland. Many men who develop prostate cancer in their 70s or 80s will die from other causes, he notes. Resnick questions whether more sensitive screening and earlier intervention would truly benefit these men, especially since 25 percent of prostate cancer patients treated by surgery or chemotherapy become impotent and up to 10 percent become incontinent.

Next January, the National Cancer Institute will launch a 16-year study to determine the extent to which quarterly screening for prostate cancer could reduce death rates from the disease, says John K. Gohagan, who will lead the $60 million project.