In a study that raised more questions than it answered, researchers have discovered a major problem in the PSA test, the standard blood screen for prostate cancer. The test measures blood levels of a protein released by the prostate. For years doctors assumed that a reading lower than 4 ng/mL of blood meant the patient was cancer free. But a study of 2,950 men published in the New England Journal of Medicine found that 15% of those with PSA levels less than 4 actually had cancer, and almost 15% of those men had "high grade" tumors, which can become aggressive. Doctors...
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