Comparison of prostate-specific antigen response in patients with metastatic castration-sensitive prostate cancer initiated on apalutamide or abiraterone acetate: A retrospective cohort study.

Background: Deep prostate-specific antigen (PSA) response (≥90% reduction in PSA [PSA90]) is an important early response indicator of radiographic progression-free survival and overall survival in patients with metastatic castration-sensitive prostate cancer (mCSPC). This study compared PSA90 responses by 6 months between patients with mCSPC at first use of apalutamide or abiraterone acetate, both androgen receptor signaling inhibitors.

Methods: Clinical data from 77 community urology practices in the United States were analyzed. Patients with mCSPC were classified into treatment cohorts based on their first filled prescription (index date) for apalutamide or abiraterone acetate on or after September 17, 2019 (approval date of apalutamide for mCSPC). Patients were followed from the index date until the earliest of index treatment discontinuation, treatment switch, end of clinical activity, or end of data availability (September 17, 2021). Inverse probability of treatment weighting (IPTW) was used to ensure similarity in distribution of baseline characteristics between cohorts. PSA90 was defined as the earliest attainment of ≥90% reduction in PSA relative to baseline (most recent value within 13 weeks pre-index). Time to PSA90 between cohorts was compared by weighted Kaplan-Meier analysis and with Cox proportional hazards models.

Results: A total of 364 patients treated with apalutamide and 147 treated with abiraterone acetate met the study criteria. Patient characteristics were well balanced after IPTW. By 6 months post-index, patients initiated on apalutamide were 53% more likely to achieve PSA90 than those initiated on abiraterone acetate (P = 0.016). Similar results were observed by 9 and 12 months post-index (both P ≤ 0.019). The median time to PSA90 was 3.5 months for the apalutamide cohort and not reached for the abiraterone acetate cohort.

Conclusions: In real-world patients with mCSPC, significantly more patients achieved PSA90 with apalutamide than with abiraterone acetate, and this response was achieved earlier with apalutamide.