Real‐World Outcomes of Radium‐223 Therapy in Metastatic Castration‐Resistant Prostate Cancer: Predictive Value of
PSA
Doubling Time and Enzalutamide Continuation
Kodai Abe, Yoshiyuki Miyazawa, Shun Nakazawa, Mai Onose, Yuta Maeno, Yusuke Tsuji, Azusa Kanayama, Akira Ohtsu, Yuji Fujizuka, Seiji Arai, Masashi Nomura, Yoshitaka Sekine, Hidekazu Koike, Hiroshi Matsui, Kazuhiro Suzuki ABSTRACT
Background
Radium‐223 dichloride (Ra‐223) is an effective treatment for metastatic castration‐resistant prostate cancer (mCRPC) with bone metastases. However, predictive factors associated with treatment efficacy remain unclear. This study evaluated prognostic factors associated with the efficacy of Ra‐223 and investigated outcomes according to enzalutamide (ENZ) combination patterns.
Methods
We retrospectively analyzed 34 patients with mCRPC treated with Ra‐223 between 2016 and 2024. Progression‐free survival (PFS) and overall survival (OS) were evaluated according to time to CRPC, pre‐treatment prostate‐specific antigen (PSA), PSA doubling time (PSADT), metastatic burden, and ENZ treatment patterns. Cutoff values were determined using the Contal–O'Quigley method. This study was approved by the Institutional Review Board of Gunma University (Approval No. 1662).
Results
The median time to CRPC, pre‐treatment PSA level, and PSADT were 17 months, 6.2 ng/mL, and 2.2 months, respectively. Shorter time to CRPC (≤ 19 months), higher pre‐treatment PSA (> 2.67 ng/mL), and shorter PSADT (≤ 2 months) were significantly associated with shorter PFS. Patients with ≥ 4 bone metastatic regions had significantly worse OS than those with ≤ 3 regions. Among the ENZ treatment patterns, continuous ENZ administration combined with Ra‐223 was associated with significantly longer PFS than discontinuation of ENZ.
Conclusions
Time to CRPC, pre‐treatment PSA, and PSADT may represent potentially useful candidate markers for identifying patients more likely to benefit from Ra‐223 therapy. Continued ENZ administration during Ra‐223 therapy was associated with favorable PFS in selected patients; however, this finding should be considered exploratory and requires validation in larger cohorts.