Background: Radium-223 (Ra-223) is a targeted alpha therapy that has been shown to prolong overall survival (OS) in patients with metastatic castration-resistant prostate cancer (mCRPC) with bone metastases. However, prognosis after Ra-223 administration varies among patients. The aim of the present study was to assess risk factors associated with the poor prognosis of patients treated with Ra-223.
Methods: We retrospectively reviewed patients' records of treatment with Ra-223 between October 2016 and December 2019. All patients had mCRPC, bone metastasis, and no known visceral metastases, and received up to six cycles of Ra-223 (55 kBq/kg). Prognostic factors for OS were analyzed by Cox proportional hazards model and log-rank test.
Results: We identified 42 patients who received at least one cycle of Ra-223 (median six cycles, range 1-6). Approximately two-thirds of patients had received at least two lines of therapy for mCRPC. The median age was 74 years, and the median follow-up duration was 13.6 months. The median OS time was 16.6 months. On multivariate analysis, PSA doubling time (PSADT) (0-3 months) at baseline, number of bone metastases (≥ 20), and treatment line of Ra-223 (4th-5th line) remained significantly correlated with the poor OS (HR 4.354, P = 0.003; HR 2.855, P = 0.020; and HR 4.871, P = 0.001, respectively).
Conclusions: Our study demonstrated that a shorter PSADT, a heavier volume of bone metastases, and a later treatment line before Ra-223 are poor prognostic factors for mCRPC patients. These newly discovered risk factors may help select patients who potentially have long-term OS after Ra-223 treatment.
Keywords: Castration-resistant prostate cancer; Number of bone metastases; Overall survival; PSA doubling time; Radium-223.