CHICAGO (Reuters) – Two large studies looking at the benefits of a common screening test for prostate cancer produced conflicting results about whether it saves lives, researchers said last week.

The studies, one in Europe and one in the United States, aim to settle a long-running debate over the benefits of a blood test called prostate specific antigen, or PSA.

Both were published online in the New England Journal of Medicine.

Early results of the US trial suggest that six years of aggressive, annual screening for prostate cancer turned up more diagnoses of prostate tumours, but no fewer deaths.

In the European trial, a less aggressive screening programme of PSA testing every four years found PSA screening cut deaths by 20 percent, but also produced a high rate of overdiagnosis.

Doctors have routinely recommended PSA tests to men over 50 in the belief that early diagnosis and aggressive treatment for any cancer is better than standing by and doing nothing.

But many prostate tumours are slow-growing and take years to cause harm. Some studies suggest many men are living with the side effects of aggressive treatment with surgery and radiation for a cancer that may never have killed them.

A US expert panel last year urged doctors to stop screening men over 75.

The US trial, led by Dr. Gerald Andriole of Washington University School of Medicine in St. Louis and colleagues, confirms that older men can skip the test.

"The important message is that for men with a life expectancy of seven to 10 years or less, it is probably not necessary to be screened for prostate cancer," Andriole said in a statement.

The US trial began in 1992 and involves 75,000 men aged 55 to 74 who got either annual PSA blood tests and rectal exams or routine care, which means they got PSA tests only if their doctor recommended them.

After seven to 10 years, overall death rates were low and there was no significant difference between the groups.

The European study began in 1990 and involves a largely white population of 162,000 men aged 55-69 from seven countries. Preliminary results found that PSA screening every four years cut prostate cancer deaths by 20 percent, offering the first data showing the tests cut the risk of death.

But earlier results from the study found about 30 percent of detected tumours are of the non-aggressive, slow-growing variety.