Independent Validation of the American Joint Committee on Cancer 8th Edition Prostate Cancer Staging Classification

Purpose: We sought to independently validate the AJCC (American Joint Committee on Cancer) 8th edition prostate cancer staging classification, which includes the elimination of pT2 subcategories and the reclassification of patients with prostate specific antigen 20 ng/ml or greater and Gleason Grade Group 5 as stage groups III-A and III-C, respectively. Materials and Methods: We identified 13,839 men who underwent radical prostatectomy at Mayo Clinic between 1987 and 2011 from our institutional registry. Outcomes included biochemical recurrence-free, metastasis-free and cancer specific survival. Kaplan-Meier analyses and Cox regression models with the c-index were used. Results: Median followup was 10.5 years (IQR 7.1-15.3). Among patients with pT2 prostate cancer the subclassification demonstrated limited discrimination for biochemical recurrence-free, metastasis-free and cancer specific survival (c-index 0.531, 0.545 and 0.525, respectively). At the same time patients with 7th edition stage group II prostate cancer and prostate specific antigen 20 ng/ml or greater had significantly worse 15-year biochemical recurrence-free survival (42.2% vs 58.8%), metastasis-free survival (78.2% vs 88.8%) and cancer specific survival (88.0% vs 94.4%, all p < 0.001) than patients with 7th edition stage group II prostate cancer and prostate specific antigen less than 20 ng/ml. However, patients with 7th edition stage group II prostate cancer and prostate specific antigen 20 ng/ml or greater had significantly better 15-year biochemical recurrence-free survival (42.2% vs 31.3%, p = 0.007), metastasis-free survival (78.2% vs 68.0%, p < 0.001) and cancer specific survival (88.0% vs 83.4%, p = 0.01) than patients with 7th edition stage group III. Also, patients with 7th edition stage group II prostate cancer and Gleason Grade Group 5 had significantly worse 15-year biochemical recurrence-free survival (37.1% vs 57.9%, p < 0.001), metastasis-free survival (63.8% vs 88.5%, p < 0.001) and cancer specific survival (73.0% vs 94.3%, p < 0.001) than patients with 7th edition stage group II prostate cancer and Gleason Grade Group 1-4 as well as worse 15-year cancer specific survival (73.0% vs 83.4%, p = 0.005) than patients with 7th edition stage group III prostate cancer. Conclusions: Our data support the changes in the new AJCC classification.