Thousands of men could be spared life-changing treatment for prostate cancer following a scientific breakthrough.
They can now find out how likely they are to die in next 10 or 15 years, and how much treatment will improve their survival chances.
For a third of prostate cancer patients, or roughly 15,000 men in Britain, the chance of dying is so low that choosing to have surgery or radiotherapy will provide little benefit.
The decision of whether to go ahead with treatment is now easier after scientists developed a computer questionnaire.
Thousands of men could be spared life-changing treatment for prostate cancer following the development of a questionnaire by Cambridge scientists
The quiz, which takes just a few minutes and should be completed with a doctor's supervision, gives men their personal odds of dying from prostate cancer or other illness over the next decade and 15 years.
They can then see a chart showing their increased chances of survival following treatment.
The results are based on men's stage of cancer, age and medical test results, and allow them to weigh up the gains against their odds of suffering erectile dysfunction and incontinence if they go ahead with surgery.
It could see more men choosing 'active surveillance', which means a doctor closely monitoring their prostate cancer instead.
Dr Vincent Gnanapragasam, from the University of Cambridge, who helped develop the questionnaire, said: 'We believe this tool could significantly reduce the number of unnecessary - and potentially harmful - treatments that patients receive and save the NHS millions every year.
'This isn't about rationing treatments - it's about empowering patients and their clinicians to make decisions based on better evidence.
A radical prostatectomy is the surgical removal of your prostate gland. This treatment is an option for curing prostate cancer that hasn't spread beyond the prostate or hasn't spread very far.
A trial showed possible long-term side effects of radical prostatectomy may include inability to get an erection and urinary incontinence.
Before having any treatment, 67 per cent of men said they could get erections firm enough for intercourse.
When the men who had a radical prostatectomy were asked again after 6 months, this had decreased to 12 per cent. When asked again after 6 years, it had slightly improved to 17 per cent.
For urinary incontinence, 1 per cent of men said they used absorbent pads before having any treatment.
When the men who had a radical prostatectomy were asked again after 6 months, this had increased to 46 per cent. After 6 years, this had improved to 17 per cent.
In extremely rare cases, problems arising after surgery can be fatal.
For many men, having a radical prostatectomy will get rid of the cancer cells. However, for around one in three, the cancer cells may not be fully removed and may return some time after the operation.
'In some cases, treatment will be the right option, but in many others, patients will want to weigh up the treatment benefits versus the risks of side effects.'
More than 47,000 men a year in Britain are diagnosed with prostate cancer, and the number of patients is predicted to rise by 69 per cent by 2030.
Currently men are classed by the NHS as being at low, intermediate or high risk from prostate cancer - a measure which evidence suggests is only accurate in 60 to 70 per cent of cases.
The new questionnaire was found to
