Authors Scosyrev E, Wu G, Mohile S, Messing EM
Review Date August 2012
Citation Cancer 2012. Published online 30 JUL 2012. DOI: 10.1002/cncr.27503
There has been much discussion recently regarding the benefits and risks of prostate-specific antigen (PSA) testing. In America the revived debate has been prompted by the US Preventive Services Task Force Recommendation Statement (2012) recommending against screening. In Australia, a debate was held at a recent prostate cancer conference on the issue of PSA testing, with prominent prostate cancer clinicians putting forward opposing views. This recent US publication in the Journal Cancer has added more data to the mix; it reports on the effect of PSA testing on incidence of advanced prostate cancer.
The objective of the study was to estimate the total number of patients who would be expected to present with metastatic (M1) prostate cancer (PC) in the modern US population in a given year if the age-specific and race-specific annual incidence rates of M1 PC were the same as the rates in the era before prostate-specific antigen (PSA) testing.
The authors computed the total number of men who presented with M1 PC in the Surveillance, Epidemiology, and End Results (SEER) 9 registries area in the year 2008 (the most recent SEER year) and estimated the number of cases that would be expected to occur in this area in the year 2008 in the absence of PSA testing. The expected number was computed by multiplying each age-race–specific average annual incidence rate from the pre-PSA era (1983-1985) by the number of men in the corresponding age-race category in the year 2008 and adding the products.
In the year 2008, the observed and expected numbers of men presenting with M1 PC in the SEER 9 registries area were 739 and 2277, respectively, with an expected-to-observed ratio of 3.1 (95% confidence interval, 3.0-3.2). If this ratio was applied to the total US population in the year 2008, then the total number of men presenting with M1 PC in that year would be equal to approximately 25,000 instead of the approximately 8000 actually observed.
The data also suggest that the benefits of screening, with respect to a reduction in risk for presenting with metastatic disease, may increase with age.
If the pre-PSA era rates were present in the modern US population, then the total number of men presenting with M1 PC would be approximately 3 times greater than the number actually observed.
Points to Note
- The observed reduction in the incidence of metastatic prostate cancer in the PSA era compared to pre-PSA era suggests that men are being diagnosed earlier with associated survival benefits, but the data must be considered in light of the limitations of an observational study.
- The study is a time-trend analysis, not a study testing causal hypotheses about effects of PSA screening, and the authors were not able to control for unmeasured factors such as changes in diagnostic techniques or changes in known or suspected risk factors for prostate cancer.
- However, the authors have done a thorough assessment of possible effects of residual confounding and lead-time bias (the effects of detection at younger ages with screening that may or may not affect survival outcomes).
- The authors acknowledge that the study could not answer the question of the optimal age for screening as they measured age at diagnosis of cancer, not age of screening, which could potentially be many years earlier in screened men.
- Despite the limitations, the authors argue that the data are useful to consider in the screening debate, particularly the apparent increase in benefit for men as they age – findings that are relevant to an ageing population.