The methodology of the PROSPER trial has previously been reported and published. In brief, men with nmCRPC, PSA doubling time ≤ 10 months, and PSA ≥ 2 ng/mL at screening were randomized in a 2:1 fashion to enzalutamide 160mg or placebo, in addition to continuing androgen deprivation therapy.
Given the primary outcome, as previously reported, of metastasis-free survival, assessment of overall survival was assessed as a key secondary outcome utilizing a group sequential testing procedure with O’Brien-Fleming-type alpha spending function. In this post-hoc analysis, the authors stratified patients into four groups on the basis of the level of PSA decline at nadir: <50% (referent), 50-90%, 90% or greater with nadir ≥ 0.2 ng/mL, 90% or greater with nadir <0.2 ng/mL. The authors used unstratified Cox proportional hazards analysis models to assess overall survival and MFS between these four groups.
Among 1,401 men enrolled in PROSPER and 933 who were treated with ENZA, PSA data were available for 905 men.
At nadir, 38% of men achieved PSA reduction ≥ 90% (actual nadir < 0.2 ng/mL), and another 27% achieved PSA reduction ≥ 90% (actual nadir ≥ 0.2 ng/mL). Among men in the placebo arm of PROSPER, only 3/457 reported PSA reduction ≥ 90%.
As demonstrated below, the depth of PSA response at nadir was strongly associated with overall survival and metastasis-free survival, with a dose-response relationship.
The authors, therefore, conclude that, among patients in the PROSPER trial receiving enzalutamide, the degree of PSA response is strongly associated with survival outcomes.
Presented by: Maha H. A. Hussain, MD, FACP, FASCO, is the Genevieve Teuton Professor of Medicine in the Division of Hematology-Oncology, Department of Medicine, and the Deputy Director at the Robert H. Lurie Comprehensive Cancer Center of the Northwestern University Feinberg School of Medicine in Chicago, IL.
Co-Authors: Cora N. Sternberg, Eleni Efstathiou, Karim Fizazi, Qi Shen, Xun Lin, Jennifer Sugg, Joyce Leta Steinberg, Bettina Noerby, Ugo De Giorgi, Neal D. Shore, Fred Saad
Written by: Christopher J.D. Wallis, Urologic Oncology Fellow, Vanderbilt University Medical Center Twitter @WallisCJD during the 2021 ASCO Genitourinary Cancers Symposium (ASCO GU), February 11th to 13th, 2021