Mortality from prostate cancer is decreasing

Comment: Using joinpoint analysis, Coory and Bade have identified a significant trend towards lower mortality rates from prostate cancer since 1994, and relate this chronologically to the increased use of prostate-specific antigen (PSA) testing in Australia. The authors raise three reasonable questions regarding this finding:

Is it plausible that the decrease could be due to some factor other than PSA testing, such as better treatment? Ecological data such as those presented by Coory and Baade are subject to the pitfalls of ecological fallacy and confounding.1 Ecological fallacy exists when there is an apparent association (eg, more men in the population screened, fewer men in the population dying), but there is no association at an individual level. Confounding would occur when there are other factors that account for the outcome, or distort the relationship between PSA testing and mortality. Treatment is one such factor, but changes in diet and other factors could also play a role (eg, lycopene from tomato-based foods2).

How do we explain these results to men who want to make an informed choice about whether to be tested? If these data were presented to men, then it would have to be explained that the data do not provide evidence of the benefits of screening and that many other factors could explain the relationship. Further, men need to be informed of the risks of false negative and false positive results associated with screening, and the risks of complications associated with treatment. It is important to assist men to make a balanced decision. Interestingly, studies in which men have been involved in such informed decisions show that information can reduce the probability that men will choose to be screened.3,4

Is this type of evidence strong enough to warrant a change in the current recommendations on PSA testing? Ecological associations generate hypotheses that are worthy of further investigation. Randomised controlled trial evidence at best, or case–control studies at least, would be required to provide evidence of the benefit of screening using PSA. Some such studies are currently in progress, including the prostate, lung, colorectal and ovarian cancer screening trial of the National Cancer Institute,5 and the European Screening Study for prostate cancer.6

Those in favour of PSA testing argue that it is the only means of diagnosing prostate cancer at an early and potentially curable stage.7 Against this is the argument that many prostate cancers are not clinically significant, as they are slow growing and will not spread, and there is a danger of diagnosis and treatment adding substantially to men's psychological and physical morbidity without benefits in terms of survival or quality of life.8 In the absence of evidence from randomised controlled trials or case–control studies, screening for prostate cancer using PSA testing remains controversial.9