The possible benefits and harms of prostate cancer screening have been hotly debated in recent years, but for the first time a new study tries to put a number on the balance of pluses and minuses for the average man.

Using data from past cancer studies and a mathematical model, researchers from the Netherlands calculated that on average, annual screening using prostate-specific antigen (PSA) testing would add three healthy weeks to a man's life.

That doesn't mean everyone should run out and get a PSA test, however.

Whether screening has a net benefit or harm for a particular man depends on how he feels about the possibility of suffering screening- and treatment-related side effects - and how much erectile dysfunction or incontinence, for example, would influence his quality of life, researchers said.

"We're even more sure than ever that it's important for doctors and their patients to talk about the prostate cancer screening decision and its potential downstream consequences," said Dr. Harold Sox, a professor of medicine at the Dartmouth Institute in Hanover, New Hampshire, who wrote a commentary published with the new study.

"Now we have some real scientific evidence that a person's choice probably should reflect what the net benefit is for them."

For the new study, Dr. Harry de Koning of the Erasmus Medical Center in Rotterdam and his colleagues built a model based on data from a European trial in which over 160,000 men were randomly assigned to undergo regular PSA testing or forgo screening.

They considered the benefits of catching some cancers early - including a lower chance of dying from prostate cancer - as well as the harms of so-called overdiagnosis. Cancers caught during screening are considered overdiagnosis if they never would have produced symptoms or threatened a man's lifespan. In those cases, treatment can cause side effects but won't do men any good.

The researchers determined that for every 1,000 men getting annual screening in their late fifties and sixties, there would be nine fewer prostate cancer deaths, 247 extra negative biopsies performed and 41 additional men getting prostate surgery or radiation. Forty-five cancers would be overdiagnosed due to screening.

Based on the effects of screening and treatment on each man's quality and length of life, those 1,000 men would ultimately gain 73 extra years of life, or 56 "quality" healthy years.

But the change in quality years due to screening could range anywhere from a loss of 21 healthy years over the 1,000 men to a gain of 97 years, de Koning's team reported Wednesday in the New England Journal of Medicine.

"Some people - we don't know how many - would actually come out negative, they would lose (quality years)," Sox said. "And other people would gain. Therefore it's hard to make one rule that would apply to everybody."

Questions, conflicting data remain

De Koning said that at the very least, his study argues against the notion that PSA screening is typically a bad idea for healthy men.

He and some of his colleagues have received consulting fees from pharmaceutical and medical device companies, including a company that designs PSA tests.

In May, the U.S. Preventive Services Task Force, a government-backed panel, recommended against PSA screening for prostate cancer in men without symptoms.

"This statement that has been around for the last couple of years now saying the benefits don't outweigh the harms - that I think is not true, it's too easy," de Koning told Reuters Health.

Still, he said, "at the individual level, you do not know whether you as the individual will get the benefits or the harms."

While the European study showed a 29-percent reduction in the chance of dying from prostate cancer in men who were screened, another large trial from the U.S. failed to show any survival benefit.

Sox said it's possible some of the figures used in the new model don't accurately reflect men's feelings about having a radical prostatectomy and ending up with erectile dysfunction and urinary incontinence, or getting radiation and developing chronic diarrhea, for example. Still, he said the study is a step in the right direction, toward appropriately weighing the long-term harms and benefits of screening.

"It's the first research article about screening that tried to incorporate the feelings of patients toward what they might experience if they underwent screening," Sox said.

"The problem (in other studies) is that the benefits are measured in one way and harms are measured another way. You end up making that judgment about whether the benefits exceed the harms, or vice versa, purely subjectively," he added.

One question that still remains is whether screening all men of a certain age is cost-effective for society, de Koning pointed out.

According to the American Cancer Society, one in six men will be diagnosed with prostate cancer at some point in their lives and one in 36 men will die of the disease.

The researchers agreed that individual men should think about how they weigh both the possible benefits and harms of getting screened for prostate cancer and discuss the decision with their doctor.

"One man might say, ‘I won't take my chances,'" de Koning said - while another will accept the risk of overdiagnosis and related side effects and still choose to get screened.