PSA Worthless for Prostate Cancer Screening?
'PSA Era Over,' Test's Pioneer Now Says
Lots of Prostate Cancers, Small Chances of Death
Prostate cancer, Stamey says, is very common. He points to autopsy data showing that while many men have prostate cancer, few die of it.
"Prostate cancer is a paper tiger in terms of the number of men who die from it," Stamey says.
PSA tests send many men to their urologists for biopsies. And these biopsies often find cancer. The question is whether these really are dangerous cancers, says Howard Parnes, MD, chief of the prostate and urological cancer research group at the National Cancer Institute.
"Sixteen percent of men in the U.S. will be diagnosed with prostate cancer," Parnes tells WebMD. "About 86% of men diagnosed with prostate cancer end up with definitive treatment, either surgery or radiation. But only 3% of these men are destined to die. ... What is scary is that if we look hard for it, if we test men every year, and if we biopsy men with a PSA over 4, we can find prostate cancer in about 25% of men."
Stamey agrees that if you look hard for prostate cancer, you'll often find it. But that alone doesn't tell doctors or patients who is at risk of dying.
"When a man submits to biopsy, he might as well be resigned to a positive result," Stamey says. "But if we don't counteract this with knowing how low the death rate is, we overestimate the significance of a positive biopsy."
PSA Still Useful
Even Stamey agrees that PSA tests are useful for some purposes, such as monitoring the success of prostate cancer surgery.
Carter argues that PSA tests aren't used properly.
"We could improve the test by focusing our efforts on younger men, where the discovery of cancer is more relevant and PSA is a much better test," he says. "But we are screening the wrong age group. We are treating the wrong age group."
Carter also argues that single PSA measurements give much less information than multiple tests. He'd like to see the test used differently.
"I think the way to use this test correctly, which gets rid of a lot of the noise in the test -- the false positives -- is to start PSA screening at age 40. Then you'd test again at age 45, and every year after 50, and put together a long PSA history. Then you could use that PSA trajectory to tell us who is gong to get into trouble."