Implications of metastatic stage at presentation in docetaxel naïve metastatic castrate resistant prostate cancer.

BACKGROUND: We performed a secondary analysis of ACIS study to determine if synchronous versus metachronous metastatic presentation has any association with survival and treatment response to dual androgen receptor axis-targeted therapy (ARAT) in docetaxel naïve metastatic castrate resistant prostate cancer (mCRPC). METHODOLOGY: In this phase III randomized controlled trial, docetaxel naïve mCRPC patients were randomized to either apalutamide or placebo combined with abiraterone and prednisone. Multivariable Cox regression models were applied to determine the adjusted association of M-stage with radiographic progression-free survival (rPFS) and overall survival (OS). To determine the heterogeneity of treatment effect based on metastatic stage (M-stage) at presentation, Cox regression was applied with interaction terms between M-stage and treatment. RESULTS: Among 972 patients, 432 had M0, 334 had M1, while M-stage at presentation was unknown in 206. There was no association of M-stage at presentation with rPFS in patients with prior local therapy (LT) (hazard ratio for M1-stage: 1.22 [95% confidence interval: 0.82-1.82]; unknown: 1.03 [0.77-1.38]) or without prior LT (M1-stage: 0.87 [0.64-1.19]; unknown: 1.15 [0.77-1.72]) with no significant heterogeneity. Similarly, there was no association of M-stage with OS in patients with prior LT (M1-stage: 1.04 [0.81-1.33]; unknown: 0.98 [0.79-1.21]) or without prior LT (M1-stage: 0.95 [0.70-1.29]; unknown: 1.17 [0.80-1.71]) with no significant heterogeneity. Based on M-stage at presentation, we did not find any significant heterogeneity in treatment effect on rPFS (interaction p = 0.13), and OS (interaction p = 0.87). CONCLUSION: M-stage at presentation had no association with survival in chemotherapy-naïve mCRPC. We did not find any statistically significant heterogeneity in efficacy of dual ARAT based on synchronous versus metachronous presentation.