Usefulness of combined androgen blockade therapy with gonadotropin-releasing hormone antagonist for bone metastatic prostate cancer with pretreatment prostate-specific antigen level ≥ 50 ng/mL

BACKGROUND: This study was performed to examine the usefulness of combined androgen blockade (CAB) therapy with a gonadotropin-releasing hormone (GnRH) antagonist (CAB-antagonist therapy), instead of CAB therapy with GnRH agonist (CAB-agonist therapy) against very high-risk prostate cancer (Pca). METHODS: We retrospectively studied 84 Pca patients with pretreatment prostate-specific antigen (PSA) level ≥ 50 ng/mL, who were pathologically diagnosed between January 2007 and December 2016. GnRH antagonist was administered to 34 patients and GnRH agonist was administered to 50 patients. All patients received concurrent antiandrogen treatment. The primary end point was PSA progression-free survival (PSA-PFS). RESULTS: PSA-PFS was significantly longer for the CAB-antagonist group compared to the CAB-agonist group (log-rank test, P < 0.01) in Pca patients with more than six bone metastases (the extent of disease [EOD] grade 2–4). On multivariate analysis, CAB-antagonist therapy was shown to be a possible prognostic factor for PSA-PFS (adjusted hazard ratio: 0.41, 95% confidence interval: 0.16–0.90, P = 0.03). CONCLUSIONS: CAB-antagonist therapy may be a useful option in bone metastatic Pca patients with EOD grade 2–4.