Scientists have just published the findings of two large trials that were supposed to tell us for certain whether screening for prostate cancer is effective. The studies seem to undercut the value of screening, but they fall short of being definitive.
The studies — one done in the United States, one in Europe — both show that screening had little or no effect in reducing prostate cancer deaths. And they raise the question, not yet definitively answered, as to whether the negative side effects from treating the discovered cancers, many of which are slow growing, might outweigh the benefits.
The primary screening tool is a blood test that detects a protein, known as prostate-specific antigen, or PSA, that is elevated when cancer is present but can be elevated for other reasons as well. A biopsy must be performed to confirm that a malignant tumor is there.
Advocates of the test argue that it can detect tumors at an early stage when they can be treated most effectively. Skeptics contend that many if not most prostate tumors grow so slowly that they would never cause symptoms during a patient’s lifetime.
Treating these indolent tumors with surgery, radiation or hormones may unnecessarily subject the patient to debilitating side effects such as incontinence, impotence, infection, painful defecation or diarrhea.
The American study, involving almost 77,000 men, found no reduction in prostate cancer deaths after all the men had been tracked for seven years and two-thirds had been followed for 10 years.
The European study, involving 182,000 men, found a modest reduction in deaths after nine years — 7 fewer prostate cancer deaths per 10,000 men screened. But there was a high risk of needless treatment given that half of the men diagnosed with prostate cancer would not have had clinical symptoms during their lifetimes. The European research suggests that roughly 50 cases of prostate cancer found through a screening program would need to be treated to prevent a single prostate cancer death.
It is possible that, as patients are followed for longer periods, more benefits may be found. Meanwhile, the advice from cancer authorities remains what it was: consult with your doctor on the pros and cons of screening. The experts can’t yet provide firm guidance.
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