Changes in conditional net survival and dynamic prognostic factors in patients with newly diagnosed metastatic prostate cancer initially treated with androgen deprivation therapy

BACKGROUND: The purpose of this study was to identify predictive factors associated with conditional net survival in patients with metastatic hormone‐naive prostate cancer (mHNPC) initially treated with androgen deprivation therapy (ADT). METHODS: At nine hospitals in Tohoku, Japan, the medical records of 605 consecutive patients with mHNPC who initially received ADT were retrospectively reviewed. The Pohar Perme estimator was used to calculate conditional net cancer‐specific survival (CSS) and overall survival (OS) for up to 5 years subsequent to the diagnosis. Using multiple imputation, proportional hazard ratios for conditional CSS and OS were calculated with adjusted Cox regression models. RESULTS: During a median follow up of 2.95 years, 208 patients died, of which 169 died due to progressive prostate cancer. At baseline, the 5‐year CSS and OS rates were 65.5% and 58.2%, respectively. Conditional 5‐year net CSS and OS survival gradually increased for all the patients. In patients given a 5‐year survivorship, the conditional 5‐year net CSS and OS rates improved to 0.906 and 0.811, respectively. Only the extent of disease score (EOD) ≥2 remained a prognostic factor for CSS and OS up to 5 years; as survival time increased, other variables were no longer independent prognostic factors. CONCLUSIONS: The conditional 5‐year net CSS and OS in patients with mHNPC gradually increased; thus, the risk of mortality decreased with increasing survival. The patient's risk profile changed over time. EOD remained an independent prognostic factor for CSS and OS after 5‐year follow‐up. Conditional net survival can play a role in clinical decision‐making, providing intriguing information for cancer survivors.