Abstract
PURPOSE: Prostate cancer epidemiology has been marked overall by a downward risk migration over time. However, in some populations, both in the United States and abroad, many men are still diagnosed with high-risk and/or advanced disease. Primary androgen deprivation therapy (PADT) is frequently offered to these patients, and disease risk prediction is not well-established in this context. We compared risk features between large disease registries from the United States and Japan, and aimed to build and validate a risk prediction model applicable to PADT patients. METHODS: Data were analyzed from 13,740 men in the United States community-based Cancer of the Prostate Strategic Urologic Research Endeavor (CaPSURE) registry and 19,265 men in the Japan Study Group of Prostate Cancer (J-CaP) database, a national Japanese registry of men receiving androgen deprivation therapy. Risk distribution was compared between the two datasets using three well-described multivariable instruments. A novel instrument (Japan Cancer of the Prostate Risk Assessment [J-CAPRA]) was designed and validated to be specifically applicable to PADT patients, and more relevant to high-risk patients than existing instruments. RESULTS: J-CaP patients are more likely than CaPSURE patients to be diagnosed with high-risk features; 43% of J-CaP versus 5% of CaPSURE patients had locally advanced or metastatic disease that could not be stratified with the standard risk assessment tools. J-CAPRA--scored 0 to 12 based on Gleason score, prostate-specific antigen level, and clinical stage--predicts progression-free survival among PADT patients in J-CaP with a c-index of 0.71, and cancer-specific survival among PADT patients in CaPSURE with a c-index of 0.84. CONCLUSION: The novel J-CAPRA is the first risk instrument developed and validated for patients undergoing PADT. It is applicable to those with both localized and advanced disease, and performs well in diverse populations.