Session: MP29: Prostate Cancer: Advanced (including Drug Therapy) II
MP29-14: Prostate-Specific Antigen Response and Time-to-Castration Resistance among Patients with Metastatic Castration Sensitive Prostate Cancer Initiated on Apalutamide, Enzalutamide, or Abiraterone Acetate
Introduction: Next-generation androgen inhibitors (AI), including apalutamide (APA), enzalutamide (ENZ), and abiraterone acetate (ABI), are approved to treat patients with metastatic castration sensitive prostate cancer (mCSPC). Among patients with mCSPC, prostate-specific antigen (PSA) response is associated with increased overall survival and decreased castration resistance (CR), an important indicator of disease progression. This study described real-world PSA response and progression to CR among patients with mCSPC treated with APA, ENZ, or ABI in the US. Methods: Data from 77 community-based urology practices (9/2018–4/2022) were used to evaluate patients with mCSPC newly initiated on APA, ENZ, or ABI using in-office dispensing data (index date is first dispensation date). On-treatment PSA response was defined as: 1) a post-index =90% decline in PSA (PSA90) from baseline (using the closest PSA value within 13 weeks prior to or on the index date) and 2) a post-index decline to =0.2 ng/mL (PSA0.2) among those with baseline PSA >0.2 ng/mL. The descriptive proportion of patients achieving a PSA response or progressing to CR was described separately for each cohort using Kaplan-Meier (KM) analysis up to 12- and 24-months post-index, respectively. Results: A total of 589 APA, 597 ENZ, and 553 ABI patients were evaluated. Mean age at index was 76 years in each group. Mean baseline PSA was 19.2 ng/mL (APA), 18.8 ng/mL (ENZ), and 24.3 ng/mL (ABI). KM rates for PSA response and progression to CR are shown in the TABLE. PSA90 by 12 months was achieved by 72% (APA), 62% (ENZ), and 55% (ABI) of patients. PSA0.2 by 12 months was achieved by 81% (APA), 63% (ENZ), and 58% (ABI) of patients. By 24 months, progression to CR was observed in 34% (APA), 39% (ENZ), and 45% (ABI) of patients. Conclusions: This is among the first observational studies to describe real-world PSA response and progression to CR in mCSPC patients treated with AIs in US community urology practices. While AIs with higher proportions achieving PSA90 or PSA0.2 were observed to have lower rates of progression to CR, further studies adjusting for baseline characteristics are needed to understand this relationship. SOURCE OF Funding: Janssen Scientific Affairs, LLC
