Outcomes of First-Line Abiraterone Acetate or Enzalutamide for Older Adults With Metastatic Castration-Resistant Prostate Cancer According to Use of Upfront Docetaxel for Metastatic Castration-Sensitive Prostate Cancer in an International Multicenter Registry: A SPARTACUSS-Meet-URO 26 Study

Background: Managing metastatic castration-resistant prostate cancer (mCRPC) in men aged ≥ 75 is challenging due to limited data. Regardless of age, in real-world clinical practice, most mCRPC still derive from failure of androgen deprivation therapy (ADT) with or without docetaxel (D) for metastatic castration-sensitive prostate cancer (mCSPC). As abiraterone acetate plus prednisone (AA) and enzalutamide (Enza) are common first-line treatments for mCRPC. The impact of prior use of D for mCSPC on the efficacy and safety of AA or Enza in this older population remains unclear. Methods: A cohort of patients aged ≥ 75 years starting AA or Enza as first-line therapy for mCRPC from January 2015 to April 2019 was identified from the registries of 10 institutions. Patients were categorized into 2 groups based on previous use of D for mCSPC. Primary endpoints were cancer-specific survival (CSS) from AA or Enza start, CSS from ADT onset, and safety. We used Kaplan-Meier method to estimate the endpoints distribution, including median values with 95% confidence intervals (95% CI). Results: Of the 337 patients identified, 24 (7.1%) received ADT+D and 313 (92.9%) received ADT alone for mCSPC. Median follow-up from AA/Enza start was 18.8 months. Median CSS from ADT or AA/Enza was not significantly different between ADT+D and ADT alone cohorts (71.9 vs. 52.7 months, P = .97; 25.4 vs. 27.2 months, P = .89, respectively). No statistically significant difference in adverse events (AEs) of any grade rate (58.3% vs. 52.1%, respectively; P = .67) or grade ≥ 3 (12.5% vs. 15.7%, respectively; P = 1.0) was found between ADT+D and ADT alone cohorts. Conclusions: Despite the innate limitations of a retrospective design and relatively small size of the ADT+D cohort, this analysis suggests that elderly men receiving AA or Enza as first-line therapy for mCRPC have similar survival outcomes and tolerability, regardless of previous D for mCSPC.