Thousands of men with prostate cancer could avoid invasive treatment and side-effects after scientists developed a personalised tool to give them a prognosis.

Every year more than 47,000 men in the UK are diagnosed with the disease. But in many cases, it is not clear how fast-growing the cancer is.

Currently, around half of patients are classed as low or intermediate risk - and left to decide if they should opt for treatment such as surgery and radiotherapy, or could safely opt to be monitored.

Treatment can carry significant side-effects, including urinary incontinence and erectile dysfunction.

Rates of treatment for cases classed as low-risk vary more than ten-fold between different hospitals, national data shows.

Scientists from Cambridge University said their new method could give individual patients a personalised survival estimate, allowing patients and doctors to make a far more informed choice.

The web-based tool, which will be offered to hospital consultants, also shows how survival for the next 10 to 15 years could change, depending on diffferent treatment options.

It also spells out the risks of different side-effects, depending on which steps are taken.

Researchers said they had developed the first personalised tool to provide such information.

Following the study, published in PLOS medicine, researchers found that doctors without access to the algorithm over-estimated the risk of death, and were far more likely to say treatment was needed, compared with those using the web programme.