A popular blood test for prostate cancer is leading many men to get treated for cancer when the treatment might not make much of a difference, according to a study in the current issue of the Journal of the National Cancer Institute.
The study's conclusions are in agreement with two earlier studies published last spring in the New England Journal of Medicine.
The PSA blood screen was once strongly promoted for all men over the age of 50, because high levels of PSA can indicate the presence of cancer. But a PSA test can't predict if treatment will be effective.
Severe Side-Effects
To come to their conclusion, H. Gilbert Welch of the Dartmouth Institute for Heath Policy and Clinical Practice and Peter C. Albertsen of the University of Connecticut School of Medicine first calculated that 1.3 million "extra" cancers were discovered after the PSA test came into use in the late 1980s.
Then they looked at cancer incidence and survival, estimating that over the years, 56,500 prostate cancer deaths were averted because of the early detection possible with the PSA test. They estimated that for every man whose life was saved by the test, 20 men were diagnosed with prostate cancer.
Surgery, radiation and drugs are often used to treat prostate cancer, but the side effects can be severe: As many as one-third of men treated have some level of impotence or incontinence, or both. The reason so few deaths were averted is because of the variability of prostate cancer.
"Some cancers grow very rapidly and kill, and they may grow so rapidly that screening doesn't really help," Welch says.
By the time they are detectable by screening, they have already spread. Other prostate cancers grow so slowly that a man is likely to die of something else before the cancer gets a chance to kill him.
Findings Pose Challenge
The findings came as no surprise to many prostate cancer researchers, because of the two studies published last spring in the New England Journal of Medicine. One study showed no difference in prostate cancer deaths among a group of men who were screened regularly, as compared to a group of men who were not screened. The other study showed only a slight advantage. This year prostate cancer is expected to kill 27,000 American men.
The findings present a challenge to physicians. There is no point to screening if men aren't going to follow up a positive result with treatment, and with treatment making so little difference, some men may not want to put up with the side effects.
Ian Thompson, head of urology at the University of Texas Health Science Center at San Antonio, says there is really only one choice about screening, and that is to explain the evidence to men, and let them make their own choices. That is the advice of the American Cancer Society and the U.S. Preventive Services Task Force.
"Two different men may look at the evidence, and one man may say a prostate cancer death is something I absolutely want to avoid, therefore I'll have a PSA," he says. "Another man might say that change in my quality of life today is more important to me."
If that man wouldn't go through treatment, then there's no point in testing him, Thompson says.
More Research
The new findings, and the ones from last spring, are sending researchers back to the drawing board.
"When the PSA test was discovered, there was enormous hope that in testing thousands and thousands of men, we'd discover cancers before they became metastatic and took the lives of patients," says Jonathan Simons, who heads the Prostate Cancer Foundation, a nonprofit group that promotes prostate cancer research.
Simons says the new research shows that more work is needed to develop a more accurate prostate cancer test.
"We've asked the PSA test to be a perfect test, and it's not a perfect cancer test," he says. "Until we can do that, we have to offer patients choices."
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