The biggest leap in diagnosing prostate cancer "in decades" has been made using new scanning equipment, say doctors and campaigners.
Using advanced MRI nearly doubles the number of aggressive tumours that are caught.
And the trial on 576 men, published in the The Lancet, showed more than a quarter could be spared invasive biopsies, which can lead to severe side-effects.
The NHS is already reviewing whether the scans can be introduced widely.
Prostate cancer is one of the most commonly diagnosed cancers for men, yet testing for it is far from perfect.
If men have high prostate specific antigen (PSA) levels in the blood, they go for a biopsy.
Twelve needles then take random samples from the whole of the prostate.
It can miss a cancer that is there, fail to spot whether it is aggressive, and cause side-effects including bleeding, serious infections and erectile dysfunction.
"Taking a random biopsy from the breast would not be accepted, but we accept that in prostate," said Dr Hashim Ahmed, a consultant and one of the researchers.
The trial, at 11 hospitals in the UK, used multi-parametric MRI on men with high PSA levels.
It showed 27 percent of the men did not need a biopsy at all.
And 93 percent of aggressive cancers were detected by using the MRI scan to guide the biopsy compared with just 48 percent when the biopsy was done at random.
Dr Ahmed, who works at University College London Hospitals, said it was "a significant step-change in the way we diagnose prostate cancer".
"We have to look at the long-term survival, but in my opinion by improving the detection of important cancers that are currently missed we could see a considerable impact," he said.
"But that will need to be evaluated in future studies, and we may have to wait 10 to 15 years."
Angela Culhane, the chief executive at Prostate Cancer UK, described the current system of testing as "notoriously imperfect".
She added: "This is the biggest leap forward in prostate cancer diagnosis in decades."
Prof Ros Eeles, from the Institute of Cancer Research in London, said the study was "very important" and "provides ground breaking data".
The chairman of the British Society of Urogenital Radiology, Dr Philip Haslam, said: "Today's findings represent a huge leap forward in prostate cancer diagnosis."
However, he warned the biggest issue could be the number of scanners and training people to interpret the results.