All men should have prostate cancer checks from the age of 40, says a leading medical group in a move that takes it even further away from the Government's position.

The Urological Society of Australia and New Zealand revised its stance yesterday, lowering to 40 the age at which it recommends men who have no symptoms first be screened for the disease, down from 50.

The Government-sponsored NZ Guidelines Group and the Cancer Society do not recommend screening asymptomatic men of any age, partly because of the risks of screening, but the Guidelines Group says men who are fully informed about the risks and benefits should be tested if they ask to be.

The Health Ministry says about half of asymptomatic men over 50 have had the prostate specific antigen (PSA) screening blood test in the past three years.

The Urological Society's statement coincided with the start of a parliamentary committee's inquiry into prostate screening and comes ahead of "Blue Friday", on which blue flags and lights in many places will mark prostate cancer awareness day.

Representing urological surgeons, the society said its advice was based on evidence that earlier diagnosis of prostate cancer reduced the risk of death from the disease.

Each year around 2500 men are diagnosed with prostate cancer, and it kills nearly 600. This is similar to the impact of breast cancer on women. Prostate cancer awareness campaigners want a men's screening scheme similar to the women's breast and cervical programmes.

But the PSA test and digital rectal examination are considered insufficiently reliable by Government agencies, and the prostate cancer treatments carry risks of side-effects such as incontinence and impotence.

One of the main screening studies relied on by the society, a large European trial, found that for every 1480 men screened, 48 would be diagnosed with cancer and one life saved. But for half of the 48, their cancer would not have developed into clinically significant disease and of them, four would be left with chronic incontinence or impotence from treatment.

In New Zealand, 2 per cent of prostate cancer deaths occur in men aged 50 to 59, and 0.2 per cent in men 40-49.

The Urological Society says men from age 40 found by screening to be at higher cancer risk should be regularly re-tested, and those at low risk should consider less frequent testing.

But cancer epidemiologist Associate Professor Brian Cox, of Otago University, said the society was out of step with the majority of cancer organisations by advocating PSA testing of asymptomatic men aged 55-69.

"Given the current conflicting evidence of any benefit from PSA testing in asymptomatic men and the known harms that can occur, it is also difficult to find value in the society's advocacy for a baseline PSA test."

The ministry noted the debate about screening asymptomatic men, and that the Guidelines Group is reviewing the latest evidence.

"Blue Friday" tomorrow will mark prostate cancer awareness day. People are urged to paint their faces blue, while 600 blue crosses will be positioned at the Te Papa Museum in Wellington to symbolise the 600 men who die every year from prostate cancer.