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

Objective 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. Methods 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. Results 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. Conclusion PSA kinetics have applications for early prognostic evaluation in Asian patients with mCSPC.