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Routine screening of men using a simple blood test can cut the death rate from prostate cancer by 20 per cent or more, according to a large and highly-anticipated European study.

The research, the most in-depth investigation to date on how prostate specific antigen (PSA) testing can influence mortality rates, provides the strongest evidence yet of the benefits of its use. But researchers added a note of caution, saying the risks and costs of PSA testing are significant, including false positives, over-treatment and the need to test massive numbers of men to prevent relatively few deaths.

"This is a landmark study. It confirms that prostate cancer can be detected early and cured," said Neil Fleshner, who holds the Love Chair in Prostate Cancer Prevention at Princess Margaret Hospital in Toronto. He said that PSA testing is an imperfect screening tool but, over all, it is as effective as programs such as mammography for breast cancer and fecal occult blood testing for colorectal cancer. "I think all men should be screened and, personally, I get screened," Dr. Fleshner said.

But Heather Chappell, senior manager of cancer control policy at the Canadian Cancer Society, interpreted the research differently, saying the impact of PSA testing on mortality was only "marginally significant ... on the cusp of happening by chance," and that the risks are greater than for other forms of screening.

The cancer society recommends that men aged 50 and older discuss the benefits and risks of PSA testing with their physician, and says that recommendation will not change based on the new findings. "We appreciate the frustration men feel, but there is no simple 'yes' or 'no' answer in this issue," Ms. Chappell said.

Bob Shiell, president of the Canadian Prostate Cancer Network, was far more unequivocal, saying the new findings are a ringing endorsement of screening and he hopes they will encourage more men to get tested. "We're big believers in PSA," he said. "It's not a perfect test, but it's the best we have." The CPCN recommends that all men get a PSA test at age 40, and have it done routinely to track any changes.

The new study, published in today's edition of the New England Journal of Medicine, was led by Fritz Schroder of Erasmus Medical Centre in Rotterdam, The Netherlands.

Researchers tracked more than 162,000 men aged 55 to 69, for almost a decade on average.

Roughly half of them took a PSA test annually, and the other half did not.

A total of 5,990 men with prostate cancer were detected in the screening group (8.2 per cent), compared with 4,307 men in the control group (4.8 per cent). (Cancers were found in the control group when the men started to experience symptoms of the disease. At that point, they were referred by their physicians for cancer-detection tests such as biopsies.)

More important, there were 261 deaths among those who were routinely screened, compared to 363 deaths in men who received routine care. That is a 20-per-cent relative reduction. Researchers predicted mortality would fall even further over time, because prostate cancer is generally slow-growing.

Dr. Schroder said, however, that the same data can be presented differently and that makes the impact of PSA testing look more modest. The study showed, for example, that 1,410 men need to be screened and 48 additional men treated to prevent one prostate cancer death, which implies a massive screening program would have a modest impact on mortality and lead to a lot of over-treatment.

Dr. Schroder stressed, too, that the reduction in mortality was limited to men in the 55-to-69-year-old age group. Most prostate cancer deaths occur in older men and many groups advocate PSA testing as young as age 40.

A second study, led by Christine Berg of the division of cancer prevention at the U.S. National Cancer Institute in Bethesda, Md. was also published today in the New England Journal of Medicine. That study, which followed almost 77,000 men aged 55 to 74 for seven years on average, found slightly more cancer in the screening group (2,820 cases or 7.3 per cent) than in the group getting routine care (2,322 cases, or 6 per cent).

There was no statistically significant difference in mortality rates between men who were screened routinely with the PSA test and those who were not in a screening program. There were 92 prostate cancer deaths in the screening group, compared to 82 in the control group.

However, PSA testing in the United States is so commonplace that many in the control group had actually been tested. Furthermore, Dr. Berg noted, there have been considerable advances in the treatment of prostate cancer in recent years, which may have "blunted any potential benefits of screening."

Dr. Fleshner said the most important issue for men is what their physicians do with the results of PSA tests. "A diagnosis of cancer does not imply treatment anymore," he said. In fact, an increasing number of men with prostate cancer opt for active surveillance, meaning their PSA levels are monitored but they do not undergo radiation or surgery. "The way I see the horizon panning out is we find more and treat less," Dr. Fleshner said.

But the new research shows that, currently at least, the men who routinely undergo a PSA test are subject to a lot more medical intervention, including more biopsies, more prostatectomies (surgical removal of all or part of the prostate gland), more radiation and more hormonal treatment.

Michael Barry, director of the health services research program at Massachusetts General Hospital in Boston, summed up the research as follows: "Serial PSA screening has at best a modest effect on prostate cancer mortality during the first decade of follow-up. This benefit comes at the cost of substantial over-diagnosis and over-treatment. It is important to remember that the key question is not whether PSA screening is effective, but whether it does more harm than good."

And that question, Dr. Barry concluded, has still not been answered definitively.

Screening, which can lead to early detection of a tumour, is complicated by the fact that prostate cancers tend to be slow-growing. That means a man might die of another cause before the prostate cancer kills him. However, in some men, the cancer can be very aggressive and life-threatening. The challenge for doctors is to identify which tumours are fast growing and require prompt medical treatment.

Prostate cancer is the most common cancer in Canadian men. In 2008, an estimated 24,700 men were diagnosed with prostate cancer and 4,300 died of the disease, according to the Canadian Cancer Society.

PSA is a protein produced by the cells of the prostate gland, a walnut-sized organ located below the bladder and in front of the rectum. PSA is normally present in the blood at low levels, defined as zero to four nanograms per millilitre. Levels of five to 10 ng/ml are considered problematic.

Increased levels of PSA may suggest the presence of prostate cancer. However, PSA levels can also be elevated due to prostate infection, irritation, benign swelling or recent ejaculation. PSA levels rise with age, and they can fluctuate. Furthermore, prostate cancer can be present without an elevated PSA level, which is why the digital rectal exam is also done as part of a routine examination.