Validation of TNM classification for metastatic prostatic cancer treated using primary androgen deprivation therapy

Purpose: The current tumor–node–metastasis (TNM) classification system has been used for many years. The prognosis of patients with metastatic prostate cancer (mPC) treated using primary androgen deprivation therapy (PADT) was analyzed according to the TNM classification. Methods: A total of 5618 cases with lymph node metastases only (N1M0), non-regional lymph node metastasis (M1a), bone metastasis (M1b), and distant metastasis (M1c) were selected from the Japanese Study Group of Prostate Cancer database. Overall survival (OS), cancer-specific survival (CSS), and progression-free survival (PFS) rates were calculated using Kaplan–Meier analysis. The influence of clinical variables on patient prognosis was evaluated using the Cox proportional hazard regression model. Results: The 5-year OS, CSS, and PFS were 76.0, 83.2, and 38.8 % in N1M0, 57.5, 69.0, and 23.0 % in M1a, 54.0, 63.1, and 23.0 % in M1b, and 40.0, 51.5, and 16.6 % in M1c, respectively. OS, CSS, and PFS worsened as the stages progressed. OS, CSS, and PFS were all significantly worse in N1M1b compared with N0M1b. Multivariate analysis revealed that OS and CSS were worse in patients with a Gleason score ≥8 and that combined androgen blockade (CAB) treatment provided better OS than non-CAB treatments at any tumor stage. However, OS and CSS were worse in individuals with a prostate-specific antigen >100 ng/ml only in M1b. Conclusions: Patient prognosis worsened with stage progression; therefore, current TNM classification system of mPC for PADT was shown to be trustworthy. Each PC cell that develops bone or lymphoid metastasis may exhibit different characteristics.