No Clear Answer In Studies Of Prostate-Cancer Test

The nation's death rate from prostate cancer has dropped 25 percent since the early 1990s, and many doctors think a blood test that measures a protein called prostate-specific antigen, or PSA, should get the credit.

But a pair of new studies — the largest ever conducted on PSA screening — calls that into question.

One study enrolled nearly 77,000 American men over age 55. The other involved 162,000 European men between 55 and 69 years old. Half of each group got regular PSA tests. The studies were designed to answer the question: Would men who got regular PSA tests have less risk of dying from prostate cancer?

The answer, after seven to 10 years of monitoring all these men, is — maybe.

In the American study, there was no difference in prostate cancer deaths between men who got PSA tests and those who didn't. In Europe, there were 20 percent fewer deaths among those who got regular PSA tests. Experts consider that difference real, but not large.

Widespread use of PSA tests might be responsible for some of the reduction in prostate cancer mortality, experts say, but better treatment seems to have played a larger role.

"This appears to be a controversy that just won't go away," says Dr. Michael Barry, a Massachusetts General Hospital researcher who has wrestled with the PSA controversy for the better part of two decades.

"Many people hoped — including me — that we might get some definitive recommendations one way or the other — you should definitely be screened, you should definitely not be screened," Barry says. "We're left somewhere in between. But that just may be the way it is."

Clearly, the effort to reduce prostate cancer mortality has a long way to go.

It's a big problem. More than 186,000 American men will get a diagnosis of prostate cancer this year; nearly 29,000 will die. One in five men faces the diagnosis over a lifetime. Baby boomer males are entering their most prostate cancer-prone years, increasing the urgency for better screening and treatment methods.

Barry says there's no doubt PSA tests can signal hidden prostate cancer. "The real question is not whether prostate cancer screening is effective," he says. "It's whether it does more good than harm."

In other words, if doctors find prostate cancer early, is it more curable? And if so, does that happen often enough to justify possible harm? That harm comes from serious side effects of surgery, radiation and drugs. Many men who wouldn't otherwise die from prostate cancer suffer these side effects.

"When we find prostate cancer, we don't know whether it's a killer cancer or what has been termed a 'toothless lion,' " explains Dr. Gerald Andriole of Washington University, the author of the new U.S. study, which cost the National Cancer Institute around $60 million. A "toothless lion" is so slow-growing that often a man will die of something else first.

Barry says it helps to compare PSA testing with breast cancer screening. Both reduce the risk of death by about the same amount — 20 percent.

Put another way, if 10,000 women are screened with mammography and breast physical exams for 10 years, seven fewer women will die of breast cancer as a result. By comparison, the new European study suggests the comparable number for prostate cancer is five lives saved for every 10,000 men screened over a decade.

But there's one big difference between breast and prostate screening. Many more men have to be treated for prostate cancer to get the same reduction in deaths. That's because fewer breast cancers are "toothless lions." They're more likely to be lethal.

"In breast cancer ... you [have to] treat about 10 women to prevent one death," Barry said. "In prostate cancer, it's about 50 men to prevent one death."

That means five times as many men will suffer from treatment side effects without benefiting.

The gap between breast and prostate cancer could be narrowed if scientists could devise a prostate screening test that identifies which tumors are dangerous. They're working on that.

Meanwhile, Andriole suggests an approach that may spare more men from unnecessary cancer treatment. First, he says, older men who have other health problems don't need to get a regular PSA test at all. Something else is likely to kill them first.

But men in their 50s and 60s pose a trickier problem. "For those patients, I would say, 'Listen, we need to know whether you're at risk for prostate cancer,' " Andriole says.

Like many American doctors, he offers them regular rectal exams and PSAs. If those show a possible problem, he'll talk with the patient about whether to do a biopsy.

But if the biopsy indicates cancer, Andriole doesn't necessarily recommend treatment right away. Instead, he monitors patients closely with rectal exams, more frequent PSA tests and biopsies to get a sense of how fast the cancer is growing.

It's called "active surveillance," and it's a growing trend. A study in the Journal of Urology this week suggests that men who choose active surveillance don't reduce their chances of a cure if their tumor later grows and they get treatment later.

Experts don't expect doctors to stop ordering PSA tests. After all, most older male physicians monitor their own PSA levels. What may change, though, is how they interpret the PSA results in light of the new studies.

Comments

 

Please keep your community civil. All comments must follow the NPR.org Community rules and terms of use, and will be moderated prior to posting. NPR reserves the right to use the comments we receive, in whole or in part, and to use the commenter's name and location, in any medium. See also the Terms of Use, Privacy Policy and Community FAQ.

Support comes from: