Radium-223 in the Third-Line Setting in Metastatic Castration-Resistant Prostate Cancer: Impact of Concomitant Use of Enzalutamide on Overall Survival (OS) and Predictors of Improved OS.

Radium-223 (Ra-223) has been recommended for bone-dominant metastatic castration-resistant prostate cancer (mCRPC). Second-generation hormone therapy in combination with Ra-223 in mCRPC has been utilized, yet its benefit has not been well elucidated. We investigated the potential survival benefit of concomitant enzalutamide with Ra-223 in the third-line setting and predictors of improved overall survival (OS).

We retrospectively identified 51 patients with bone-dominant mCRPC that were treated with Ra-223 in the postchemotherapy and post-hormone therapy setting, either alone (group A; n = 32) or with concomitant enzalutamide (group B; n = 19). The primary endpoint was to study the OS difference between groups A and B. The secondary endpoint was to identify predictors of improved OS with Ra-223 in the third-line setting.

Mean age was 70.9 years, median baseline prostatic-specific antigen (PSA) was 23.1 ng/mL, alkaline phosphatase was 91 IU/L, and hemoglobin was 12.5 g/dL. There was no difference in median OS between groups A and B, at 20.4 versus 17.5 months, respectively (P = .5186). In univariate and multivariate analyses, only pre-Ra-223 PSA < 30 ng/mL and Eastern Cooperative Oncology Group performance status < 2 were associated with improved OS.

In our study cohort, concomitant use of enzalutamide with Ra-223 in the mCRPC setting was not associated with improved OS. Only pretreatment PSA < 30 ng/mL and pretreatment Eastern Cooperative Oncology Group performance status < 2 were associated with improved OS. Further prospective studies are warranted.

Clinical genitourinary cancer. 2021 Jan 07 [Epub ahead of print]

Mohamed E Ahmed, Vidhu B Joshi, Mohamed Badawy, Lance C Pagliaro, R Jeffrey Karnes, Val Lowe, Matthew P Thorpe, Eugene D Kwon, A Tuba Kendi

Department of Urology, Mayo Clinic, Rochester, MN. Electronic address: ., Department of Urology, Mayo Clinic, Rochester, MN., Division of Nuclear Medicine, Department of Radiology, Mayo Clinic, Rochester, MN., Division of Hematology and Medical Oncology, Department of Internal Medicine, Mayo Clinic, Rochester, MN.