Clinical outcomes of abiraterone acetate (AA) or enzalutamide (E) as first-line therapy (Rx) for men aged ≥75 with metastatic castration-resistant prostate cancer (mCRPC) according to previous use of docetaxel (D) for metastatic castration-sensitive prostate cancer (mCSPC) in a multicenter international registry: A SPARTACUSS – Meet-URO 26 study.

Abstract

107 Background: The optimal management of mCRPC in men aged ≥75 is challenging, and there is a paucity of clinical data in the literature. Although AA and E are commonly used as 1st line Rx for mCRPC, it is unclear whether use of upfront D for mCSPC may impact their clinical efficacy or safety in this elderly population. Methods: Patients aged ≥75 who started AA or E as 1st line Rx for mCRPC within January 2015 - April 2019 were identified from the IRB approved databases of 10 institutions in Europe, South and North America. Demographic and clinicopathological data were collected from available medical records, including Gleason, prior local therapy, newly diagnosed metastatic disease, disease volume, ECOG, PSA and sites of metastases. Patients were classified by use of upfront D for mCSPC. The primary endpoints were overall survival (OS) from AA/E onset and OS from ADT start and safety of AA/E. The endpoints distributions including median (95% CI) were estimated by Kaplan-Meier method. Results: Of the 337 patients selected, 24 (7.1%) received ADT+D and 313 (92.9%) ADT alone for mCSPC. Patients with ADT+D tended to be younger (78 vs 81, p=0.022) and, albeit not statistically significant, had higher rates of Gleason score >8 (81.0% vs 62.6%, p=0.10), newly diagnosed (83.3% vs 65.6%, p=0.08) and high volume disease (45.8% vs 34.6%, p=0.28), compared to those with ADT alone. Median follow-up was 18.8 months. No significant difference of OS from ADT start or from AA/E onset was observed between the 2 cohorts (see table). Despite OS from ADT start being longer in those having ADT+D, OS from AA/E start was approximately 2 years in both cohorts. Rates of adverse events (AEs) of any grade (58.3% vs 52.1%, p=0.67) and grade ≥3 (12.5% vs 15.7%, p=1.0) did not significantly differ between the 2 cohorts. Conclusions: While limited by small sample size for ADT+D and retrospective study design, patients aged ≥75 having AA/E as 1st line mCRPC Rx showed similar survival outcomes and tolerability regardless of previous use of D for mCSPC. [Table: see text]