(UroToday.com) The 2022 GU ASCO Annual meeting included a prostate cancer session featuring work from Dr. Benjamin Lowentritt and colleagues presenting results of a comparison of patients initiated on apalutamide or enzalutamide for metastatic castration sensitive prostate cancer (mCSPC) and the outcomes of patients attaining an early, deep PSA response. Deep PSA response, defined as a ≥90% decline in PSA (PSA90), is an important early prognostic factor for achieving radiographic progression free survival and overall survival in patients with mCSPC treated with a next generation androgen receptor inhibitor (ARI) or androgen biosynthesis inhibitor. This study compared PSA90 responses among patients with mCSPC at first use of a next generation ARI.
Clinical data from 69 community urology practices in the United States were evaluated. Patients with mCSPC were classified into treatment cohorts based on their first filled prescription (index date) for apalutamide or enzalutamide after December 16, 2019. Patients were followed from index date until the earliest of index regimen discontinuation, treatment switch, end of clinical activity, or end of data availability (March 5, 2021). Included patients had ≥12 months of clinical activity to assess baseline characteristics. Inverse probability of treatment weighting (IPTW) was used to reduce baseline confounding by controlling for age, race, index year, ADT use ≥6 months, first-generation antiandrogen use, most recent PSA level, most recent testosterone level, Gleason score, and time between metastasis and the index date. PSA90 was defined as the earliest attainment of ≥90% decline in PSA relative to baseline PSA (most recent value within 13 weeks pre-index). The proportion of patients achieving a PSA90 and the time to PSA90 was compared using a weighted Kaplan-Meier analysis and weighted Cox proportional hazards models.
A total of 186 apalutamide patients and 165 enzalutamide patients met the study criteria. Patients’ characteristics were generally well balanced after IPTW. In both weighted cohorts, the mean age was 76 years, 71% were white, and the mean baseline PSA level was 18 ng/mL. By 6 months, 73.6% of apalutamide and 69.5% of enzalutamide patients had a post index PSA measurement. At 6 months, significantly more mCSPC patients initiated on apalutamide attained PSA90 response than patients initiated on enzalutamide (p=0.014). This result continued to remain significant at 9 months and at the end of the follow-up:
The median time to PSA90 was 3.1 months for apalutamide patients and 5.2 months for enzalutamide patients.
Dr. Lowentritt concluded this presentation comparing real-world patients initiated on apalutamide or enzalutamide for mCSPC with the following take-home messages:
- In this real-world study of patients with mCSPC, significantly more patients attained an early and deep PSA90 response when treated with apalutamide relative to enzalutamide
- PSA90 response was attained significantly earlier in patients treated with apalutamide than with enzalutamide
- The proportions of patient attaining a PSA90 response by 6 and 12 months following initiation of apalutamide are consistent with those observed in the TITAN phase 3 study1 (68% and 71%, respectively)
- The clinical implications of these observations warrant further consideration given existing evidence on the association of rapid, deep, and durable PSA response with survival-related endpoints in patients with these medications
Presented by: Benjamin Lowentritt, MD, Chesapeake Urology, Towson, MD
Co-Authors: Dominic Pilon, Ibrahim Khilfeh, Carmine Rossi, Erik Muser, Frederic Kinkead, Dexter Waters, Lorie Ellis, Patrick Lefebvre
Written by: Zachary Klaassen, MD, MSc – Urologic Oncologist, Assistant Professor of Urology, Georgia Cancer Center, Augusta University/Medical College of Georgia, @zklaassen_md on Twitter during the 2022 American Society of Clinical Oncology Genitourinary (ASCO GU) Cancers Symposium, Thursday, Feb 17 – Saturday, Feb 19, 2022