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A study released today confirms that prostate cancer may be present even among patients with ''normal'' scores on the PSA, or prostate-specific antigen test. Researchers say the findings show that a better screening test is needed.
Although several factors influence a man's risk of developing prostate cancer, many doctors agree that scores above 4 on the common screening test may indicate cancer.
Doctors who studied nearly 3,000 men found cancers in 15% of those with PSA levels below 4, according to research in today's New England Journal of Medicine. The risk of prostate cancer rose with increasing PSA levels.
When examined under a microscope, however, relatively few of these cancers were found to be dangerous.
The study's authors note that the PSA test gives doctors few clues about which cancers will ever threaten a man's life. High scores can be caused by many conditions, from cancer to infections or a benign swelling of the prostate gland that is common in older men.
Doctors note that prostate tumors, especially those found early, are often slow-growing and are not life-threatening.
Autopsy studies have found that nearly 30% of men in their 30s and 40s have prostate cancer, although they may not know it, says Len Lichtenfeld, deputy chief medical officer for the American Cancer Society. About two-thirds of men in their 60s and 70s may have the disease.
More than 230,000 men will be diagnosed with the disease this year, and 30,000 will die from it, the National Cancer Institute says.
Critics note that the PSA misses some early cancers. Earlier studies found cancers in more than 20% of men with PSA scores of 2.5 to 4.
Some experts say such findings illustrate the need for more aggressive screening and treatment. The National Comprehensive Cancer Network, a group of 19 leading hospitals, recommended earlier this year that doctors should consider biopsies for men with PSA scores above 2.5.
The authors of today's study, however, say such thresholds may no longer be very useful.
''There is no magic cutoff below which a man can assume he is completely free of risk or above which he must feel compelled to have a biopsy,'' says Howard Parnes, a study author and chief of the cancer institute's prostate and urologic cancer research group. ''We need to allow each man, with the help of his physician, to assess his own risk.''
The researchers noted that men and their doctors need screening tests that differentiate aggressive tumors from those that pose less of a threat.
Results from the ongoing Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial -- a study of 75,000 men that aims to determine whether prostate screening saves lives -- are expected within five years, Parnes says. Scientists at the institute and other universities also are working to develop better screening tests.
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