Two recent studies from Europe and the US have not provided equivocal evidence about whether prostate cancer screening helps - but the fault may be in the study designs

Many men over fifty get a regular blood test to check their Prostate Specific Antigen (PSA) level in the belief that detecting an increase in PSA will ensure early detection of prostate cancer.

Given the fact that Prostate cancer is one of the most commonly diagnosed cancers in men - and a common cause of cancer death in men - deciding to have a blood test to diagnose this malignant disease in its early and curable stages is understandable.

However, there has been controversy as to whether subjecting a population to such screening tests is beneficial.

Doctors were hoping that two large long term studies whose results were expected this year would provide the necessary information on which to base advice about prostate cancer screening. It was hoped that the results of these two trials would either show such a great benefit that the decision to undergo a screening test would be completely justified - or that they would show that screening gave no benefit whatseover, so that doctors could confidently tell their patients that screening is a waste of time and money.

Unfortunately, the trial results so far have left doctors still scratching their heads!

The European study which was published in the New England Journal of medicine in March 2009 involved over 162,000 men from seven countries aged 50 to 74 years who had a blood test for PSA done on average once every four years. After a median follow up of nine years, it was found that screening allowed identification of cancers with a reduction in deaths from prostate cancer by about 20 per cent in the screened population when compared to the non-screened population.

The American study, published in the same issue of the Journal, involved over 76,000 men between 55 and 74 years who had an annual blood test for PSA for six years, together with an annual rectal examination for four years. This study in contrast found no difference in mortality after a follow up period of 7 to 10 years.

One drawback is that both trials used a low cut off point for the PSA blood test to decide on whether to subject the patient to a prostate biopsy - 4 microgram/litre in the US study and 3 microgram/litre in the Euroepan study.

A PSA level of 4 was the threshold, anything above which was considered abnormal and an indication to subject the man to a prostate biopsy. This figure of 4 was derived from a research study in the nineteen eighties that utilised one of the earliest PSA assays. Today we know that the normal PSA level rises with age - and using an age-related guide as to what level can be considered ‘Normal’ at various ages is one method of interpreting a man’s blood level of PSA more accurately.

While PSA is a protease that is specifically produced by the prostate gland, it is not specifically produced by cancer cells - so that a raised level of PSA does not necessarily mean prostate cancer. Moreover, there are prostate cancers that can develop in men even without a rise in PSA. This considerable overlap in PSA levels in men with and without prostate cancer makes it difficult to separate ‘normal’ from ‘abnormal’ values.

The discovery of PSA was a major advance in that it was the first test that allowed doctors to detect early curable prostate cancer. Research is now underway to try and refine the use of PSA - such as using the rate of rise of PSA, the ratio of free to total PSA, or even identifying a more cancer-specific component of PSA to help obtain a more accurate assessmentof the malignant potential of a prostate gland.