Prostate‐specific antigen kinetics in Asian patients with metastatic castration‐sensitive prostate cancer treated with apalutamide in the TITAN trial: A post hoc analysis

In the TITAN trial of patients with metastatic castration-sensitive prostate cancer (mCSPC), deep and rapid prostate-specific antigen (PSA) decline with apalutamide plus androgen deprivation therapy (ADT) was associated with longer overall survival (OS), radiographic progression-free survival (rPFS), time to PSA progression (TTPP), and time to castration resistance (TTCR) compared with no decline (all p < 0.0001). This post hoc analysis evaluated PSA kinetics in the Asian subpopulation. Data were analyzed for patients enrolled in China, Japan, and Korea and treated with apalutamide (n = 111) or placebo (n = 110) plus ADT. Examined were depth of PSA response, rates of PSA decline, and associations between a deep PSA response and clinical outcomes in apalutamide-treated patients. Confirmed PSA response rates were higher with apalutamide than placebo: 73.9% versus 33.6% for PSA ≤0.2 ng/mL, 90.1% versus 58.2% for PSA reduction ≥50% [PSA50], and 74.8% versus 25.5% for PSA reduction ≥90% [PSA90]. Median (Q1; Q3) time to PSA ≤0.2 ng/mL, PSA50 and PSA90 response in the apalutamide group was 1.9 (1.0; 3.7), 1.0 (1.0; 1.0), and 1.8 (1.0; 1.9) months, respectively. PSA responses with apalutamide or placebo were consistent irrespective of high- or low-volume disease. Achievement of confirmed PSA ≤0.2 ng/mL or PSA90 response with apalutamide at landmark 3 months was associated with significantly (nominal p-values) longer OS (hazard ratio: 0.23; p = 0.0009), TTPP (0.16; p = 0.0001), TTCR (0.20; p < 0.0001), and time to progression on first subsequent therapy or death (0.19; p < 0.0001) compared with no decline. PSA kinetics have applications for early prognostic evaluation in Asian patients with mCSPC.