BLOOD TEST FOR PROSTATE CANCER LAUDED

Researchers reported Wednesday the first strong evidence that a widely used blood test for prostate cancer accurately detects a significant majority of cancers that will later grow, spread and become deadly. The news should ease nagging doubts about the test that have troubled many doctors and patients.

The test was also found to have a low false-positive rate, cases in which cancer is detected in men who do not have it, leading unnecessarily to further tests and treatment.The test, known as PSA, for prostate specific antigen, could find 80 percent of aggressive prostate cancers five years before they would otherwise have been detected and could find half of all aggressive prostate tumors 10 years before they would have been noticed.

But the study, published in The Journal of the American Medical Association, did not address the pressing question of whether treating prostate cancer early saves lives.

In some cancers, like lung cancer, even early detection and treatment do not make a difference in survival rates. Because the treatment for prostate cancer has many serious side effects, including incontinence and impotence, the debate over the use of the test continues.

For years, medical experts have argued over the value of the PSA test. On the one hand, all agree on the importance of reducing the death rate from prostate cancer, which is the second leading cause of cancer deaths in men, after lung cancer.

On the other hand, many say the test should not be used for widespread screening unless two things can be proved: that the PSA finds cancers that are deadly and that treating those cancers saves lives. The new study addresses the first of these concerns.

Prostate cancer was diagnosed in about 200,000 men in 1994, and in two-thirds of the cases the cancer had already spread beyond the prostate gland by the time it was diagnosed. But the cancer can also be indolent, and it often is, causing no symptoms and never spreading. Autopsy studies show that 30 percent of men have prostate cancer when they die, although most never know it.

The study, by Dr. Charles Hennekens of Harvard Medical School and Brigham and Women's Hospital in Boston, involved data from a continuing research project, the Physicians' Health Study. It includes 22,071 doctors who were 42 to 84 years old in 1982.

At the start of the study, each man provided blood samples that were stored in liquid nitrogen. Hennekens and his colleagues identified men in whom prostate cancer was diagnosed after enrolling in the study and did PSA tests on their stored blood.