Prostate cancer mortality in New Zealand: the past and projections for the future.

Abstract

Ageing male populations and improved diagnosis of early stage disease have contributed to the increasing incidence of prostate cancer observed in many Western countries. The clinical significance of these diagnosed cancers is, however, currently unclear. The aim of this study is to examine trends over time in prostate cancer mortality as an indicative measure of clinically significant disease during a 29-year period (1965-93) which preceded the extensive use of early cancer diagnostic techniques or radical therapy protocols. Age-specific and age-standardized rates were calculated for each year during the study period, using routinely collected mortality and demographic data. A Poisson regression model was used to describe trends in the age-specific rates over time to predict numbers of prostate cancer deaths and the lifetime risk of death over the next 20 years. Significant annual increases ranging from 1 to 2.6% were found for age-specific prostate cancer mortality rates over the 29-year time period, with the largest increases experienced in the younger age groups at risk. Based on projected population ageing and growth alone, annual numbers of prostate cancer deaths are predicted to increase from 487 in 1993 to 664 by the year 2006 and then to 833 by the year 2016. Continuation of the observed increases in age-specific mortality rates would result in a predicted 797 deaths by the year 2006, while an expected 1115 deaths is calculated for the year 2016. This would correspond with an increase in the lifetime risk of death from prostate cancer from a present 3.7 to 4.5% in 10 years and 6.2% in 20 years. The changing pattern of prostate cancer mortality described in this study is likely to represent a significant increase in the incidence of clinically significant disease. This will have a significant impact on the ageing New Zealand male population, and important implications for the provision of effective treatment and preventive strategies.