Deep, rapid, and durable prostate-specific antigen decline with apalutamide plus androgen deprivation therapy is associated with longer survival and improved clinical outcomes in TITAN patients with metastatic castration-sensitive prostate cancer

Background: The first interim analysis of the phase III, randomized, double-blind, placebo-controlled, multinational TITAN study demonstrated improved overall survival (OS) and radiographic progression-free survival (rPFS) with apalutamide added to ongoing androgen deprivation therapy (ADT) in patients with metastatic castration-sensitive prostate cancer. The final analysis confirmed improvement in OS and other long-term outcomes. We evaluated prostate-specific antigen (PSA) kinetics and the association between PSA decline and outcomes in patients with metastatic castration-sensitive prostate cancer from TITAN. Patients and methods: Patients received apalutamide (240 mg/day) or placebo plus ADT (1: 1). This post hoc exploratory analysis evaluated PSA kinetics and decline in relation to rPFS (22.7 months’ follow-up) and OS, time to PSA progression, and time to castration resistance (44.0 months’ follow-up) in patients with or without confirmed PSA decline using a landmark analysis, the Kaplan–Meier method, and Cox proportional hazards model. Results: One thousand and fifty-two patients (apalutamide, 525; placebo, 527) were enrolled. Best confirmed PSA declines (≥50% or ≥90% from baseline or to ≤0.2 ng/ml) were achieved at any time during the study in 90%, 73%, and 68% of apalutamide-treated versus 55%, 29%, and 32% of placebo-treated patients, respectively. By 3 months of apalutamide treatment, best deep PSA decline of ≥90% or to ≤0.2 ng/ml occurred in 59% and 51% of apalutamide- and in 13% and 18% of placebo-treated patients, respectively. Achievement of deep PSA decline at landmark 3 months of apalutamide treatment was associated with longer OS [hazard ratio (HR) 0.35; 95% confidence interval (CI) 0.25-0.48), rPFS (HR 0.44; 95% CI 0.30-0.65), time to PSA progression (HR 0.31; 95% CI 0.22-0.44), and time to castration resistance (HR 0.38; 95% CI 0.27-0.52) compared with no decline (P < 0.0001 for all). Similar results were observed at landmark 6 and 12 months of apalutamide treatment. Conclusions: Apalutamide plus ADT demonstrated a robust (rapid, deep, and durable) PSA decline that was associated with improved clinical outcomes, including long-term survival.