Prostate cancer accounts for a quarter of cancers in men
The prostate cancer death rate in the US has fallen since screening became more common, but that does not prove such tests are needed, a study argues.
Since screening became widespread in the US, mortality rates have fallen four times more than in the UK.
But writing in the respected Lancet Oncology, a UK team said many other factors could be at play.
These include different treatment programmes for US men, and discrepancy over how deaths are reported.
Many men over 80 have evidence of prostate cancer when they die, but it can be unclear whether this or other conditions killed them - leading to different accounts on death certificates.
This does not mean that screening - using a blood test to detect what is known as the prostate specific antigen (PSA) - is not saving lives, the team from the University of Bristol acknowledge.
But until studies pin down the exact role of screening in decreasing prostate cancer mortality, "we can only continue to speculate", they wrote.
Prostate cancer screening took off in the US in the early 1990s, and by 2001, nearly 60% of men over 50 said they had undergone the test in the previous 12 months.
By contrast in the UK, between 1999 and 2002, an estimated 6% of men aged 45-84 had been tested.
At the beginning of the 1990s, mortality rates for the two countries were broadly similar. But after this period, the rate of decline in the US - at 4.17% per year, was almost four times that of the UK, at 1.17% per year.
But other changes were occurring in the treatment of men with prostate cancer in the US, the team led by Simon Collin noted.
These included the use of a particular hormone treatment in older men and more aggressive treatment of those with an advanced form of the disease.
Prostate cancer is the most common cancer in men in the UK, but the NHS has shied away from offering screening.
This is because the test is seen as notoriously inaccurate: although 10-15% of men will have high enough PSA levels to warrant carrying out a prostate biopsy, only 2-3% will require any treatment.
The majority will have undergone unpleasant, invasive and potentially costly investigations for no reason.
John Neate, head of The Prostate Cancer Charity, said the findings of studies from Europe and the US looking at whether the test really was saving lives were keenly awaited.
"Whatever the results of these major trials however, there is an urgent need for a new diagnostic test which could form part of a national screening programme and which would reliably identify the aggressive prostate cancers that need treatment.
"This would enable us to focus treatment on those men who need it and allow men with non-aggressive prostate cancers to avoid the risks and side effects of diagnostic procedures and treatments," he said.
A spokesperson from the NHS cancer screening programmes said: "All screening programmes are based on an assessment that more good than harm will be achieved through their implementation.
"Until there is clear clinical evidence to show real benefit can be gained from routine prostate screening, the NHS will not be inviting men who have no symptoms for prostate cancer screening."