Early Detection

Better tests for prostate cancer

Almost 60,000 American men will develop cancer of the prostate this year, and more than 20.000 will die of the disease. At least half of those deaths might have been avoided had the cancer been diagnosed sooner. In its earliest stages, it can usually be arrested by prompt and aggressive surgery or radiation, or both. The catch is that early detection has so far proved difficult, not only because men too often avoid rectal examination by the physician's gloved finger, but because available blood tests turn up evidence of malignancy in only more advanced cases.

One important early warning sign of prostatic cancer has been recognized for 40 years: a marked rise in the bloodstream of an enzyme--acid phosphatase--produced by the prostate gland. As the disease progresses, the level continues to rise. The challenge has been to develop tests sensitive and reliable enough to detect the increase before the cancer spreads. Now. in a sudden spurt of research activity at several medical centers, at least two promising new techniques are being tested.

Studying 113 men with prostate cancer, researchers from the Southern California Permanente Medical Group and U.C.L.A. turned to the radioimmunoassay. which can detect incredibly small quantities of biological substances with the help of radioactive tracers. The results: they were able to identify the telltale phosphatase elevation in the blood of 33% of patients in the early, first stage of the disease. 79% of second-stage cases. 71% third stage and 92% of the cases in the fourth and final stage--when the disease is often far too advanced for any hope of cure. By contrast, they report in the New England Journal of Medicine, the traditional blood test for prostatic cancer, which involves color measurement of a product of the enzyme's activity, identified the rise of enzyme levels in only 12%, 15%, 29% and 60% of their patients at corresponding stages of the disease.

Comparable results have been obtained at Roswell Park Memorial Institute in Buffalo and Columbia-Presbyterian Medical Center in Manhattan. There, scientists use the reaction in an electric field between the patient's blood and serum from immunized rabbits to determine acid phosphatase levels.

Some 90% of the prostatic cancers now discovered are diagnosed only after the malignancy has spread beyond the prostate gland. But concludes a New England Journal editorial, "The clear indication is that mass screening on the basis of a blood test alone can reverse this gloomy experience."

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