Screening for prostate cancer helps prevent deaths from prostate cancer, according to a new analysis in the Annals of Internal Medicine.

That may seem like common sense. Yet whether prostate-specific antigen (PSA) testing—which checks your blood for the presence of a protein that can indicate prostate-cancer risk—actually saves lives has been the subject of controversy for nearly two decades.

The two most comprehensive trials of prostate cancer screening, both published in 2009, came to conflicting conclusions. One, from the U.S., found that the screening had no benefit; another, from Europe, found that it reduced prostate cancer deaths by 20 percent.

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This new study does provide some clarity about the benefits of screening, and suggests that the U.S. study underestimated the test's ability to save lives, says Ruth Etzioni, Ph.D., a biostatistician in the public health sciences division of the Fred Hutchinson Cancer Research Center and one of the study’s 22 authors. 

But the new study doesn't resolve another long-held concern about PSA testing: That it identifies many men with unaggressive cancers that would never harm them, yet who undergo aggressive treatments that often leave them impotent, incontinent, or both.

“Men considering prostate cancer screening should understand not just the potential, small benefits of the test, but the significant harms associated with it, too,” says Marvin M. Lipman, M.D., Consumer Reports’ chief medical adviser.

That's why Consumer Reports—along with the American Cancer Society, the American Academy of Family Physicians, and several other groups—has long cautioned men against rushing into routine prostate cancer screening, but instead urges them to first have full, thoughtful conversations with their doctors about the risks and benefits of the test.

Here's what you need to know about this new study, so you can use its findings to help you make an informed choice about whether prostate cancer screening is right for you.

Reconciling the Conflicting Evidence

The new study, conducted by researchers from the University of Michigan, the Fred Hutchinson Cancer Research Center, the National Cancer Institute, and several other research institutions in the U.S. and Europe, re-analyzes data collected in the two 2009 trials.  

It takes into account what turned out to be a major problem with the U.S. study that found PSA tests had no benefit.

Normally in a clinical trial, scientists compare what happens to people who receive a test or treatment—in this case, prostate cancer screening—to those who don’t. 

In the 2009 U.S. study, scientists compared people assigned to receive prostate cancer screening to those receiving the regular care they would get from their doctors. The trouble, Etzioni says, is that by the time that study got underway, that "regular care" often included prostate cancer screening.

Scientists have since learned that as many as 85 percent of  participants who were assigned to the non-screening group had received at least one PSA test over the course of the  trial. So—predictably, in retrospect—they found little difference between the two groups.

The new study used statistical analysis to correct for that problem. It found that the U.S. study actually agreed with the results of the European study showing that prostate cancer screening does save lives.

However, the absolute benefit still isn’t large, Etzioni notes.

Without any screening, she says, research shows that out of 1,000 men, about 25 to 30 will die from prostate cancer. This study shows that with screening, about 18 to 23 men would have died; in other words, that out of every 1,000 men screened, the test might save about about seven lives.

The Harms of Prostate Cancer Screening

While the new analysis has helped clarify the potential benefits of prostate cancer screening, the risks of the test are already well documented.

Several studies have shown that the test causes many men to be treated unnecessarily—at great cost, and considerable physical and psychological harm.

Here's why. Many cases of prostate cancer grow slowly enough that they probably would be unlikely to harm a man during his lifetime. And though doctors can sometimes tell which cancers are slow-growing and which are more aggressive, that's not always possible. In addition, some men may prefer to treat a non-aggressive cancer, "just in case" or for peace of mind.

Etzioni says estimates vary, but her group has projected that for every man whose life is saved through prostate cancer screening, about five may be diagnosed and potentially treated unnecessarily for cancers that would never have harmed them—a phenomenon known as overdiagnosis and overtreatment.

Prostate removal surgery, a common method of treatment, carries real risks: According to the U.S. Preventive Services Task Force (USPSTF), an independent group supported by the U.S. Department of Health and Human Services that develops recommendations on preventive healthcare, as many as one in three men who undergo the surgery will experience erectile dysfunction, and one in five will experience urinary incontinence.

That means many men who would have been just fine without treatment may be left with permanent health problems.

What This Means for You

 The USPSTF is currently updating its guidelines on prostate cancer screening, but the draft recommendation says that men aged 55 to 69 should discuss the harms and benefits of screening with their doctor, and come to an individual decision about whether screening is right for them.

Lipman says that even in light of new Annals study, that advice remains sound. “You need to have a long conversation with your doctor about whether the potential harms of screening are worth the risk,” he says, adding that the emphasis should be that most cancers detected by the PSA test will be slow-growing and never cause harm.

And most experts agree that men 70 and older generally should not be screened. That's because screening is especially unlikely to detect a cancer that would harm a man if he’s already over 70, explains Andrew Vickers, Ph.D., a biostatistician with the Memorial Sloan Kettering Cancer Center who wrote an editorial accompanying this new research.

He also recommends men considering the test ask themselves this question: “What would happen if the doctor found a low risk cancer?”

If you’re someone who thinks you would be satisfied with keeping an eye on the low-risk cancer but not treating it right away, screening may be a good option for you. A 2016 study in the New England Journal of Medicine found little difference in prostate cancer survival rates between men aged 50 to 69 who underwent treatment for prostate cancer and those who chose surveillance of the disease rather than treatment.

But if you think you wouldn’t be able to resist going ahead with aggressive treatment for even a slow-moving cancer, Vickers says, you may be better off delaying screening.