It is strongly argued that a wide-ranging screening program should be established to try and limit prostate cancer deaths. The issue of whether or not screening for prostate cancer will affect death rates is debated with some acrimony. Currently 1 – 2% of UK males and 20% of US males are screened.
Prostate cancer screening consists of the measurement of the prostate specific antigen (PSA) and a rectal examination. PSA is a protease, an enzyme that breaks down proteins, which is made almost exclusively by the prostate and it functions in maintaining the patency of the prostatic ducts. It is relatively non-specific as a tool for the detection of prostate cancer. It is an inaccurate and insensitive test, as levels are elevated in benign prostatic hypertrophy and prostatitis. The normal PSA value for the diagnosis of prostate cancer is > 4 ng/ml. But at raised levels between 4-10ng/ml just 25% of patients will have prostate cancer, and at levels between 10 and 40 ng/ml only 40% will have prostatic cancer.
It is not clear how frequently PSA should be measured but a recent report indicates that bi-annual screening reduces mortality.
The lack of specificity of PSA for the early detection of prostate cancer was first described in the Physicians’ Health Study, in an analysis of 22,071 male physicians who had been recruited to a prospective study. Over a ten year period of follow-up, 520 men developed prostate cancer. PSA levels when measured in serum stored at the start of the study were elevated in 46% of patients, so that in 54% there was no clue from PSA that a cancer was about to develop.
Screening in the UK
The situation with regard to screening in the UK is not clearly defined, because of the lack of specificity of PSA as a diagnostic test and the enormous expense of screening and then treating “normal” men. Attempts have been made to screen just the relevant populations at risk for prostate cancer and by so doing increase diagnostic specificity. Despite all the arguments used by clinicians against screening, there remains a strong argument from the patients’ hearts that screening reduces death rates from prostate cancer. The patients’ view may also be correct, because a European study of prostate cancer screening has recently reported a decrease in both distant and early stage disease, together with a decline in prostate cancer mortality.
One of the reasons for the delay in the implementation of screening for prostate cancer is that it has not been proven in any randomised study that the early treatment of asymptomatic localised prostate cancer decreases death rates. Medicine lives on proof, and objective proof comes from randomised trials. At diagnosis, treatment options include radical surgery, radiotherapy and observation where treatment is given if the patient develops symptoms. These treatments have never been compared in a trial involving significant patient numbers and so we have to rely on unreliable evidence.
It is clear that a significant proportion of early stage prostate cancer is indolent and will not impact upon the lives of the vast majority of patients. However there is a significant proportion of patients whose tumours, regardless of microscopic appearances, have a more aggressive character. It is not possible to distinguish between these two groups using current tests.
Meanwhile, the argument from the heart faces the rationalists. The argument from the heart says, “it must be better to catch a cancer early”; whilst the rationalists say, “it’s not been proven in prostate cancer.”