Screening men for prostate cancer does not result in a significant difference to mortality rates, according to a large new study funded by Cancer Research UK.
The research was carried out by scientists at the Universities of Bristol and Oxford and included more than 400,000 men aged 50 to 69 in the UK.
Some 189,386 participants who were invited to have a one-off Prostate Specific Antigen (PSA) test were compared with 219,439 men who did not attend screening.
After a follow-up period of ten years - making this the largest ever prostate cancer trial - there were 8,054 cases of the cancer in the screened group and 7,853 in the non-screened group. This rate of 4.3 per cent and 3.6 per cent was not deemed to be statistically significant.
Importantly, both groups registered the same number of men dying from prostate cancer: 0.29 per cent of the sample.
Writing in the Journal of the American Medical Association, the researchers said this suggests that testing men without symptoms for PSA detects some diseases that may not have caused harm, but also misses some particularly aggressive prostate cancers.
They warned that finding non-significant cancers could lead to anxiety over cancer, the potential for infection after a biopsy and possibly even side-effects such as incontinence following treatment including chemotherapy.
Lead author of the report Professor Richard Martin said: "We found that offering a single PSA test to men with no symptoms of prostate cancer does not save lives after an average follow-up of ten years. The results highlight the multitude of issues the PSA test raises."
He added that Cancer Research UK is now funding studies that will follow the men for longer in a bid to see whether the tests have any impact on mortality further down the line.
Co-author of the report Dr Emma Turner said: "We now need to find better ways of diagnosing aggressive prostate cancers that need to be treated early."
This may include identifying faulty genes that make some men more likely than others to develop prostate cancer.
Overdiagnosis of cancer has been receiving more attention in recent years, particularly since many autopsy-based studies have shown dormant cancers lying within people who died from other causes. This suggests that people can live without being aware of a cancer, or harmed by it.
"The Holy Grail is finding something that tells us which cancers are harmless and which aren't, and then we can distinguish between them and ignore the harmless ones," said Cancer Research UK's Professor Peter Sasieni.