Screening men for prostate cancer could reduce deaths from the disease by a fifth despite doubts about the diagnostic test used, a major study has found.
The positive effect of screening increased over time, the research involving more than 162,000 men showed.
Over a period of nine years, screening reduced the number of men dying from prostate cancer by 15%, increasing to 22% after 11 years.
During the whole 13-year follow-up period, the risk of death was 21% lower in men who were screened than in those who were not.
Screening for prostate cancer is controversial because the initial diagnostic test patients have, to measure blood levels of the biomarker prostate specific antigen (PSA), is so unreliable.
Higher than normal PSA readings can be obtained from healthy men, and low readings from individuals with cancer. For this reason, routine screening for prostate cancer is not carried out in the UK.
The European Randomised study of Screening for Prostate Cancer (ERSPC) recruited men aged 50 to 74 from eight European countries - Belgium, Finland, France, Italy, the Netherlands, Spain, Sweden and Switzerland.
Even though the findings demonstrated that screening reduced deaths, the authors said it was still too soon to introduce population-wide screening.
Lead researcher Professor Fritz Schroder, from Erasmus University Medical Centre in the Netherlands, said: "PSA screening delivers a substantial reduction in prostate cancer deaths, similar or greater than that reported in screening for breast cancer.
"However, over-diagnosis occurs in roughly 40% of cases detected by screening resulting in a high risk of over-treatment and common side-effects such as incontinence and impotence."
" The time for population-based screening has not arrived. Further research is urgently needed on ways to reduce over-diagnosis preferably by avoiding unnecessary biopsy procedures, and reducing the very large number of men who must be screened, biopsied, and treated to help only a few patients."
The findings, published in The Lancet medical journal, prompted a similar reaction from Prostate Cancer UK.
Dr Iain Frame, the charity's director of research, said: "Ou r ability to identify those most at risk of aggressive prostate cancer through a national screening programme is a topic high on most people's agendas.
"These results are no great surprise and highlight yet again the urgent need for a test which can distinguish between dangerous cancers that could go on to kill and those which may never cause any harm.
"Without a reliable test, the introduction of a screening programme could mean an enormous rate of over-diagnosis and therefore over treatment of potentially harmless cancers - outweighing any benefits that a screening programme might bring.
"Getting an accurate diagnostic test that can be delivered relatively cheaply and simply could mean that the UK can start thinking about the introduction of a national screening programme and our research is working towards that.
"However, in the meantime, men most at risk of prostate cancer - black men, men over 50 and men with a family history of the disease - should speak to their GP about their risk and whether the PSA test is right for them."
Advanced types of magnetic resonance imaging (MRI) scans may offer a way of selectively diagnosing aggressive prostate cancers, said Prof Schroder.
A Department of Health spokesman said: " All men should have clear information so they can weigh up the risks and benefits of having a prostate specific antigen (PSA) test for prostate cancer. Materials have been sent to GPs in England so they can help men make this decision.
"We are also providing £35 million for a major trial on the best form of treatment for prostate cancer and investing an additional £450 million to help diagnose cancer earlier in order to help save thousands of extra lives every year."