For men with metastatic hormone-sensitive prostate cancer (mHSPC), enzalutamide with androgen deprivation therapy (ADT) offers longer radiographic progression-free survival (rPFS) compared with placebo and ADT, regardless of baseline prostate-specific antigen level (PSA), based on results from the phase 3 ARCHES trial.
Although initial PSA level was not predictive of response, treatment with enzalutamide and ADT improved PSA-related efficacy measures, reported lead author Arnulf Stenzl, MD, of the University of Tübingen, Germany, and colleagues. The adverse effect profile of enzalutamide was similar to previous experiences with castrate-resistant patients, they noted in their abstract, which was presented at the annual meeting of the American Urological Association.
ARCHES was a double-blind, placebo-controlled trial involving 1,150 patients with mHSPC, divided approximately 1:1 to receive either enzalutamide with ADT (n = 574) or placebo with ADT (n = 576). Eligibility required that patients had not exhibited radiographic disease progression or rising PSA levels for up to 3 months of ADT, or up to 6 months with prior docetaxel. The primary endpoints were death within 24 weeks of stopping treatment and rPFS. Treatment was continued until unacceptable toxicity or disease progression. PSA levels were measured at baseline and at follow-up, which was an average of 14.4 months.
Median baseline PSA level across both cohorts was 5.21 ng/mL, with most patients having received prior ADT (91%). Baseline PSA was not predictive of response, “suggesting the limitation of baseline PSA as a predictive factor in this population in which most [patients] received prior ADT,” the investigators wrote. Although PSA levels were not predictive, enzalutamide did have a greater impact on PSA-related efficacy endpoints; compared with the placebo group, patients in the enzalutamide arm were significantly more likely to have PSA reductions from baseline of at least 50% (92.9% vs. 56.8%) and at least 90% (72.8% vs. 30.0%). In further support of the efficacy of enzalutamide, median rPFS in the enzalutamide group was significantly better than in the placebo group (not reached vs. 19.4 months). Adverse events were comparable between enzalutamide (85.1%) and placebo (85.9%) cohorts.
Astellas Pharma and Medivation funded the study. The investigators reported no conflicts of interest.
SOURCE: Stenzl et al. AUA 2019. Abstract LBA-10.