Background: Recently approved oral therapies APA and ABI (plus prednisone) are effective mCSPC treatments. Prior real-world evidence showed that, relative to ABI, patients who initiated APA had significantly higher rates of PSA decline ≥90% (PSA90), which has been associated with longer overall survival. The objective of this study was to compare PSA90 response among an enhanced cohort of patients with mCSPC initiated on APA or ABI. Methods: Electronic medical records from PPS Analytics including data from US community urology practices were linked with administrative claims from the Komodo Health Solutions Research Database. Androgen receptor signaling inhibitor (ARSI)-naïve patients with mCSPC with ≥12 months of pre-index clinical activity were selected into the APA or ABI cohort based on their first paid claim/dispensation on or after 17 Sep 2019 (index date). Patients were followed to earliest of index ARSI discontinuation or switch, radiopharmaceutical use, end of insurance or clinical activity, or end of data availability (30 Sep 2022). Inverse probability treatment weighting (IPTW) was used to reduce potential pre-index confounding, controlling for age, race, region, insurance payer, index year, time from metastasis to index date, time from first prostate cancer (PC) diagnosis to index date, metastasis locations, de novo PC, use of androgen deprivation therapy, first-generation antiandrogens or chemotherapy, most recent PSA and testosterone levels, and most recent Gleason score. PSA90 was defined as the earliest attainment of ≥90% decline in PSA relative to pre-index (most recent value within 13 weeks). The proportion of patients achieving PSA90 was compared using a weighted Kaplan-Meier analysis and the time-to-PSA90 response was compared using a weighted Cox proportional hazards model. Results: A total of 917 APA and 632 ABI patients were identified. Patient characteristics were balanced with IPTW (Table). By 6 months post-index, 80.9% of APA and 72.8% of ABI patients had a PSA measurement. By 6 months, significantly more APA patients attained a PSA90 response, as compared to ABI patients (P < 0.001; Table). Median time-to-PSA90 was 3.5 months for APA patients and 8.8 months for ABI patients. Conclusions: This real-world study supports previous findings that a greater percentage of patients with mCSPC in the US initiating APA achieved deep PSA response compared to those initiating ABI.

*Concurrent prednisone use was not required for inclusion to ABI cohort.