In what has been described by experts as a ''game changing'' finding, American researchers tracked the progress of 731 men with prostate cancer over 12 years to see how surgical removal of the prostate compared with ongoing observation of the cancer to see if it became more active or spread.

The largest clinical trial comparing the two approaches to date found surgery did not significantly change the survival rate between the groups. After a decade, 21 men or 5.8 per cent of those who received surgery had died from prostate cancer or its treatment compared with 31 or 8.4 per cent of those whose doctors watched their progress.

The researchers said the difference could have been due to chance and not significant enough for surgery to be advised. The number of Australian men having PSA (prostate specific antigen) tests and surgery for prostate cancer has increased dramatically over the past decade as high-profile men such as Sam Newman and Alan Jones have publicised their prostate cancer diagnoses.

In the study's surgery group, one in five men suffered a complication from the surgery called a radical prostatectomy. Two years on from the procedure, one man had died from it, 81 per cent suffered erectile dysfunction, 17 per cent had urinary incontinence and 12 per cent bowel dysfunction. In the observation group, 44 per cent had erectile dysfunction, 6 per cent urinary incontinence and 11 per cent bowel dysfunction.

The researchers found that for men with early-stage cancer that had not spread from the prostate, radical prostatectomy did not significantly reduce the chance of death over 12 years.

The findings, published in the New England Journal of Medicine, add to growing concern that the use of unreliable PSA tests is causing over-diagnosis of prostate cancer, which in most men will be so slow-growing it will not cause them harm. In Australia, doctors say about 20,000 men are diagnosed with prostate cancer each year, including one in six with an aggressive form.

But because it is difficult to tell which of the remaining cancers will progress to cause trouble or not, many men are choosing treatments that can cause them harm, including thousands who choose surgery.

Cancer Council chief executive Professor Ian Olver said a large European study had shown that for every man whose life was saved by a radical prostatectomy, 37 men had one that did not save their life. ''I can't imagine the figure is any different in a similarly developed country like Australia,'' he said.

However, Professor Olver said thousands of men still died from prostate cancer every year and surgery was likely to help those with an aggressive form.

Head of urology at Royal Melbourne Hospital Professor Tony Costello said about a quarter of Australian men being diagnosed were choosing observation. In the remaining three-quarters, he said about 80 per cent were opting for surgery.

Professor Costello said Australian surgeons had much lower complication rates than those in the American study, with about 30 per cent suffering erectile dysfunction and 5 per cent incontinence two years after surgery.