Real-world burden of adverse events for apalutamide- or enzalutamide-treated non-metastatic castration-resistant prostate cancer patients in the United States

BACKGROUND: Second-generation androgen receptor inhibitors (ARIs) have been associated with adverse events (AEs) such as fatigue, falls, fractures, and rash in non-metastatic castration-resistant prostate cancer (nmCRPC) patients as identified in clinical trials. The objectives of this study were to describe the incidence and management of AEs in patients receiving apalutamide and enzalutamide. METHODS: This retrospective chart review study was conducted in nmCRPC-treating sites in the United States. Patients starting apalutamide or enzalutamide between February 1, 2018 and December 31, 2018 were included and any AEs they experienced were recorded. AEs, including those considered to be of special interest as defined in the pivotal clinical trials of the second-generation ARIs, were analyzed and grouped retrospectively in this study. Detailed chart data (patient demographics, clinical characteristics, treatment history, type of AE, outcomes, and resource utilization) were then collected for a randomly selected subset among patients with ≥1 AE to characterize AEs and their management. Descriptive results were summarized. RESULTS: Forty-three sites participated in the study. A total of 699 patients were included, of whom 525 (75.1%) experienced ≥1 AE. The most common AEs were fatigue/asthenia (34.3%), hot flush (13.9%), and arthralgia (13.6%). In the subset of 250 patients randomly selected from those who experienced ≥1 AE, patients were primarily White (72.0%), the mean age was 71 years, 86.0% had an Eastern Cooperative Oncology Group score of 0–1 at nmCRPC diagnosis, and the average prostate specific antigen (PSA) value at diagnosis was 23.2 ng/mL. PSA-doubling time < 10 months was chosen as reason to initiate treatment in 40% of patients. The median duration of follow-up was 1.1 years, with 14.4% of patients progressing to metastasis by end of study period. Grade 3–4 and Grade 5 AEs occurred in 14.4 and 0.4% of patients, respectively. Actions taken to manage AEs included AE-directed treatment (38.0%), ARI discontinuation (10.4%), dose reduction (7.6%), and AE-related hospitalization (4.8%). CONCLUSIONS: This study highlights the burden of AEs among nmCRPC patients treated with apalutamide or enzalutamide, providing a relevant real-world benchmark as clinical trial evidence and the treatment landcape for nmCRPC continues to evolve.