Unmasking A Stealthy Cancer

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More than any other malignancy, cancer of the prostate has a reputation for stealth. While 122,000 American men were diagnosed with the disease last year -- making it the leading cancer among men -- 70% of those tumors had already managed to spread beyond the gland and into the rest of the body without being detected. Frustrated surgeons have long hoped for a test that could pick up more of these cancers before they become inoperable. Now they may have got their wish. Researchers reported in last week's New England Journal of Medicine that a new method could potentially spot 20% to 30% more cancers than do rectal exams alone, the current means of early tumor detection.

The simple $50 test, based on a protein called prostate-specific antigen, or PSA, will soon be offered to men over 50 who are at special risk for the disease, including blacks and those with a family history of the ailment. Some experts contend that all older men should be tested. Predicts lead author Dr. William Catalona, at Washington University in St. Louis: "PSA should dramatically alter the statistics on prostate cancer."

Rectal examinations have been the standard for early diagnosis for nearly a century. But this method, in which doctors probe the prostate gland manually, has not been very popular with patients or their doctors. In West Germany, where men over 40 can be tested for free, a recent study found that only 15% actually agreed to have it done. Physicians point out that the exams often fail to detect smaller cancers and those that originate on the front of the gland. The method is also subjective. One expert remarked that all he can tell his medical students is that the gland feels "like the soft skin at the base of the thumb" while a tumor feels "like a knuckle." Concluded Dr. William Cooner, a PSA expert at the University of South Alabama: "The rectal examination has served us very poorly." Several alternatives have been tried over the years, the most recent being an ultrasound probe. Although this proved somewhat effective and is now used to confirm diagnoses, at $200 to $300 an exam it is too costly to use for routine screening.

The basis for the new assay, PSA, is a protein produced by cells on the surface of the prostate and thought to play a role in preventing semen from coagulating. An enlarged prostate (due to cancer or other problems) leads to higher levels of PSA in the blood. Doctors already use PSA tests to monitor the effectiveness of prostate-cancer therapies, such as irradiation or hormonal treatments. Some researchers have argued that the exams should replace much more expensive bone scans as a way of determining how far the cancer has spread.

But the method is by no means foolproof. Catalona stresses that 21% of the men in his study with prostate cancer actually had "normal" PSA levels. Thus the test should be used only in combination with a rectal exam, he said, and even then some cancers will be missed.