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

Background: 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. Methods: 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. Results: 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%). Conclusions: 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. Impact: Evaluation of the effectiveness of PSA screening would require a comprehensive analysis of changes in mortality, survival, and treatment practices over time.