Prostate cancer is an interesting disease. In Europe and North America, it is the most frequently diagnosed cancer in men and one of the leading causes of cancer death in men. In 2007, worldwide there were 670,000 men diagnosed with the disease. Deaths are more difficult to ascertain as many men diagnosed with early prostate cancer die with rather than of the disease. Like breast cancer, there are major differences in rates between different countries. Some of these differences appear to be driven by differences in rates of use of a blood test for prostate-specific antigen (PSA) which will detect early cancers and can be used as a screening test.
Prostate-specific antigen is made by the prostate and is a protein whose normal function is to liquefy the fluid produced during ejaculation (an aside – rodents do not make PSA and produce a solid semen plug during intercourse, yet mice are widely used in prostate cancer research). PSA is found in small quantities in the blood in men without cancer. In the presence of a prostate cancer (but also in other diseases affecting the prostate), larger amounts are liberated into the bloodstream, enabling the measurement of PSA to be used as both an early diagnostic and monitoring test for prostate cancer. Since the early 1990s, the test has been, increasingly, widely available and used both for screening for undiagnosed cancer and as a tool for monitoring the response of cancer to treatment. In the USA, the test has been widely available from a range of sources and is actively promoted to the public by the makers of test kits – knowledge of your PSA level has become something men need to be aware of in the same way that cholesterol used to be. In the UK, until recently, government policy discouraged ‘opportunistic’ PSA testing, and there was no systematic screening programme on the grounds that there was no evidence that early diagnosis of prostate cancer reduced death rates from the disease. Recent data from screening trials suggest that PSA testing may reduce deaths from prostate cancer, but that around 40 men need to be treated for PSA-test-detected cancer in order to save 1 life. Whether this level of benefit will result in screening programmes, being set up remains to be seen. It should be noted that this is similar to the level of benefit from breast cancer screening. Although widely applied, the benefits of screening are therefore not nearly as clear cut as may be imagined from the very widespread application of breast cancer screening across the Western world. For the time being, PSA testing is variable across the world and largely consumer driven.
If we start by looking at diagnosis and death rates from prostate cancer, some very obvious differences are seen (Figure 1).