Prostate cancer screening is usually done by measuring levels of prostate specific antigen (PSA) in the blood.  A PSA level of more than 4 ng/mL may indicate the presence of cancer.  Sometimes prostate cancer screening also involves a digital rectal exam,  where the doctor feels to see if the prostate is enlarged.  The problem is that the value of prostate cancer screening has not yet been established and men need to be aware of this if they are thinking of getting a PSA test.

Some large-scale trials of prostate cancer screening have been carried out and have reported results recently. In one of them, the European randomised study of screening for prostate cancer (ERSPC), 162,000 men received either PSA testing each year for four years or no screening.  Screening did reduce deaths from prostate cancer, but you would need to screen 1410 men to prevent just one death.  The other trial, known as the prostate, lung, colorectal and ovarian cancer screening trial (PLCO) involved 76,000 men and was terminated early (after ten years follow up) because there was no difference between the men receiving prostate cancer screening and those not receiving it. In terms of mortality.  The researchers even believe screening can be harmful.

These new findings have prompted Dr David Neal of the Department of Oncology,  University of Cambridge, UK, and colleagues, to write in The Lancet   about the prostate cancer screening controversy.  The root problem with prostate cancer screening is that it is neither sensitive nor specific enough.  One third of men with PSA levels between 3 and 10 ng/mL have prostate cancer.  We cannot define a lower limit below which there is no risk – because 18% of men with levels between 1 and 3 ng/mL have cancer which may even be high grade.  Nor is it yet clear how best to treat prostate cancer detected by screening, which has not given rise to symptoms.  Some of these cancers are low risk and a man could live his whole life without knowing he had the disease (and die of something else).  Yet some men, once diagnosed with cancer, will not be able to rest till it is ‘rooted out’ and they will opt for radical surgery, which is linked to severe side effects. What is required is a better version of the PSA test, or a replacement based upon an alternative biomarker.  Meanwhile, a man thinking of having a PSA test ought to be sure he is properly informed before going ahead.

Source   

Neal DA et al Screening for prostate cancer remains controversial The Lancet October 31 2009 374;1482-1483