Long-term Trends in Prostate Cancer Incidence by Stage at Diagnosis in Japan Using the Multiple Imputation Approach, 1993–2014

Abstract

This study aimed to assess long-term trends in the incidence of prostate cancer by stage at diagnosis before and after the introduction of population-based PSA screening. We used data from three population-based cancer registries in Japan. A total of 29,458 malignant prostate cancer cases diagnosed between 1993 and 2014 were used for the analysis. Multiple imputation with chained equations was used to impute a specific stage at diagnosis for cases with "unknown" and missing status. We estimated the age-standardized incidence rates by stage at diagnosis from 1993 to 2014, and used joinpoint linear regression models to assess changes in trend. Joinpoint analyses after imputation showed that localized cancer was stable from 1993 to 2000, followed by a pronounced but insignificant increase through 2003 (from 12.1 per 100,000 in 2001 to 34.1 per 100,000 in 2003), and a significant increase thereafter [annual percentage change (APC), 4.1%]. For regional cancer, the imputed data showed that the increasing trend lasted from 1993 to 2006 (APC, 12.5%), then leveled off through 2014. For distant prostate cancer, the imputed data showed the increasing trend continued from 1993 to 2004 (APC, 2.4%), and started to marginally decline thereafter (APC, -2.2%). Our study confirmed a significantly rapid increase in localized prostate cancer after the spread of PSA screening in Japan, with a marginal decrease in distant prostate cancer after 2004. Evaluation of the effectiveness of PSA screening would require a comprehensive analysis of changes in mortality, survival, and treatment practices over time.