Screening for prostate cancer using prostate specific antigen (PSA) would lead to a substantial number of tumours diagnosed at an earlier and more treatable stage, but there would be likely cases of overdiagnosed prostate cancer, according to a study published in the British Journal of Cancer.

The researchers studied 43,842 healthy men given PSA testing as part of the ProtecT study to calculate the number of advanced stage prostate cancers picked up as a result of the testing. They also worked out the length of time during which prostate tumours do not produce symptoms but are detectable by a screening test – the mean sojourn time (MST). The MST test is a method of calculating ‘overdiagnosis’ and was used to estimate the probability of a diagnosis of prostate cancer which would not have caused symptoms during the patient’s lifetime if screening had not taken place.

Some 1,544 men aged 50-69 were diagnosed with prostate cancer through the PSA testing. Overdiagnosis was estimated at one in 10 in the 50-59 age group and increased to three in 10, (31 per cent) in the 60-69 age group.

However, after adjusting for overdiagnosis, two-yearly PSA testing might still result in a reduction in advanced stage prostate cancer of up to 54 per cent.

Study author, Dr Nora Pashayan, a Cancer Research UK scientist at the University of Cambridge, said: “Our results indicate a benefit of screening to reduce the risk of advanced stage prostate cancer. However, this is limited by overdiagnosis. Any screening strategy should take account of the potential benefits and harms of screening. A valuable target for future research would be to estimate the benefit of screening at different ages.”

Prostate cancer can be slow-growing or aggressive. Men with a non-aggressive form may not develop symptoms for many years and not always need treatment - the side effects of which can be significant. But the difficulty is that on diagnosis, doctors can not always tell which forms of prostate cancer are aggressive and which are slow-growing.

Lead author Professor David Neal, based at Cancer Research UK’s Cambridge Research Institute, said: “Overdiagnosis is a real concern. There is currently no way to tell whether a prostate cancer is aggressive, or passive.

“Until a test has been developed to distinguish between these, we would prefer to avoid treating patients who don’t need treatment – because it can lead to unnecessary side effects like impotence and incontinence. It is important that men in their 50s and 60s feel able to talk to their doctors and request a PSA test if necessary.”

There is no prostate cancer screening programme in the UK but there is ongoing ad-hoc testing. Screening with PSA alone is not yet recommended in the UK because there is not yet firm evidence that screening reduces mortality from the disease.

Prostate cancer is the most common cancer in men in the UK – more than 34,000 men are diagnosed each year and 60 per cent of cases are diagnosed in men over 70. Around 70 per cent of newly diagnosed prostate cancer patients live longer than five years.

Professor Peter Johnson, Cancer Research UK’s chief clinician, said: “We need to continue to search out markers that will tell us if a prostate cancer is aggressive or not so that we know which ones to treat and which ones are best to monitor.

“While a recent important European study shows that PSA tests can detect very early prostate cancer and may reduce deaths from the disease by up to 20 per cent, even in large trials it has been difficult to prove the real impact of PSA screening. We need to monitor the results with longer follow up.

“We still don’t know how best to approach treatment for early disease, and it’s important we find answers to this as soon as possible through research funded by Cancer Research UK and others.

“The important thing is that any men that think they might be experiencing symptoms such as difficulty urinating should contact their GP as soon as possible to rule out cancer.”