But it's not quite that simple.
Those extra years of high-quality life showed up across big groups of screened men. Individual men may get different results -- especially if screening-associated risks such as impotence and incontinence bother them more than the possible benefit of a life free of prostate cancer.
Whether to get a PSA test is a tricky decision.
Urologists, who see men dying of late-stage prostate cancer, tend to favor PSA screening for all men as they reach middle age. They want to catch the cancers while they are still treatable.
Testing experts, including the U.S. Preventive Services Task Force, calculate that the real harms of prostate cancer over-diagnosis and over-treatment outweigh potential benefits. It's an ongoing debate.
The new study, published today in the New England Journal of Medicine, "moves the ball down the field quite a lot," according to medical decision-making expert Harold C. Sox, MD, professor of medicine at Dartmouth's Geisel School of Medicine.
PSA Pluses and Minuses
Harry J. de Koning, MD, professor of public health and screening evaluation at the Netherlands' Erasmus Medical Center, led a team that analyzed data from a large European clinical trial of PSA screening. They translated all outcomes of regular PSA testing into quality life years gained or lost.
"I think prostate cancer screening has been shown to be effective, but there are a lot of negative side effects," de Koning tells WebMD. "What we now say is that a man age 55 to 69, if he is screened every four years, will gain something like 8.5 years of life. But we say you should diminish this by 20%, to about 6.7 years, because then you get healthy life years. It is a longer life, but a mix of good things and bad things."
De Koning and colleagues arrived at their calculation by assigning life-quality values to each possible outcome of PSA screening.
"So a person who just got a biopsy thinks, 'Today is 10% worse than my average day in life.' Maybe some say 20% or 40%. That is what we try to calculate," de Koning says. "Or if a man is getting palliative care for metastatic cancer and you ask how much worse this state is than normal, he may say it's 50% worse than two years ago when he was healthy."
These values, while reasonable and based on previous quality-of-life research, clearly would vary from person to person. They calculate that 1,000 men who receive PSA screening would gain 56 years of high-quality life. But they note that if slightly different values were used, these 1,000 men might lose as many as 21 quality life years or gain as many as 97.
That gap makes it impossible to recommend for or against PSA screening for all men, says Sox, whose editorial comments accompany the de Koning report in the NEJM.
"If a significant number of men could end up losing quality life years as a result of their feelings about the kind of side effects that can happen with prostate cancer treatment, a significant number of patients also would gain quality life years by not worrying about dying of prostate cancer," Sox tells WebMD. "So you can't have a general recommendation either for or against PSA testing. You have to talk to the patient and find out what his feelings are."
PSA Decision: Case by Case
That's almost exactly the current recommendation of the American Cancer Society. Unlike the U.S. Preventive Services Task Force, which based on its own risk/benefit analysis flatly advises men not to get the test, the ACS advises men to sit down with a medical professional and discuss all the risks and all the benefits.
That's not very satisfying to men who want protection from prostate cancer, but who don't want to gamble on a test that might lead to severe side effects from unnecessary treatment.
And there's the rub. De Koning and colleagues note that in the European study, 42% of cancers detected by PSA screening were "over-diagnosed" -- that is, they never would have done harm.
"Strategies to reduce over-diagnosis would seem to be necessary before screening can be generally advocated," they write.
Until this happens, Sox recommends improving our "meager" understanding of how men feel about the quality of their lives after treatment for prostate cancer.