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Estimated impact of the prostate cancer prevention trial on population mortality

We believe there is a critical error in the recent publication by Unger et al. that in our opinion invalidates their conclusion that the prevention of low-grade prostate cancer with finasteride would save more than 300,000 person-years of life in the U.S. The model presented by Unger et al. estimated the effect of finasteride treatment on mortality based on differences in survival between men with and men without prostate cancer. However, their analysis did not consider the fact that survival depends significantly on age. In their analysis, the life expectancy of men without prostate cancer appears to be based on the experience of all men age 55 years; however, men diagnosed with prostate cancer are on average much older. In U.S. census data, 40% of men age 55 years are age 65 years, whereas in the U.S. population-based Surveillance, Epidemiology, and End Results (SEER) cancer registry, only 25% of men age 55 years who are diagnosed with localized prostate cancer are age 65 years. Therefore, the projected benefit in the analysis by Unger et al. stems from shifting approximately 25% of men diagnosed with prostate cancer to a survival distribution for men who are considerably younger. By comparing prostate cancer patients who are older with men from the general population who are younger, we believe the authors overestimated the potential person-years saved with finasteride. The results of the analysis by Unger et al. are very different when recalculated using appropriately age-matched populations. The overall 10-year survival for men diagnosed with low-grade prostate cancer in the SEER registry was reported to be 60%. However, the 10-year survival for identically age-matched men in the general population using data from the National Center for Health Statistics is reportedly only 57% (Fig. 1). Therefore, on average, we find that men diagnosed with low-grade prostate cancer are more likely to be alive at 10 years compared with men without prostate cancer. This unexpected result appears to be due to overdiagnosis and a healthy screening effect. Therefore, even when survival curves are properly matched for age, the benefit of prevention cannot be measured by simply comparing survival data for prostate cancer patients with that for men in the general population. We believe that, ultimately, if there is any population mortality benefit derived from preventing low-grade prostate cancer, it will only be realized 10 or more years after the disease would otherwise have been diagnosed.