Cutoff Value of Time to Prostate-specific Antigen Nadir is Inversely Correlated with Disease Progression in Advanced Prostate Cancer

To identify the early predictor of progression to castration-resistant prostate cancer (CRPC) for different stage of advanced PC patients, we focused on time to prostate-specific antigen (PSA) nadir following primary androgen deprivation therapy (PADT). We reviewed 184 advanced (locally advanced and metastatic) PC patients (101 patients with bone metastasis (BM) and 83 patients without BM at presentation) who had received PADT at our institution. We evaluated laboratory data, pathological results, and the influence of PSA kinetics impact on disease progression. The progression rates were analyzed with reference to the nadir PSA level and time to PSA nadir (TTN) following PADT by Kaplan-Meier method. In all, 103 patients (56%) progressed to CRPC. Nadir PSA lower than 0.2 ng/ml (nadir ≤0.2) during PADT was observed in 114 patients (62%). Median TTN was 8.5 months in patients with BM and 11.5 months in patients without BM. Multivariate analysis revealed that nadir ≤0.2 following PADT (P<0.001), longer TTN (>8 months) (P<0.001), extent of disease on bone scan grade (P=0.02), and T stage (P=0.04) in BM group and nadir ≤0.2 following PADT (P<0.001), longer TTN (>11 months) (P<0.001), and T stage (P=0.03) in without BM group were independent prognostic factors for progression. In both groups, longer TTN identified patients with prolonged progression-free survival in both nadir ≤0.2 and >0.2 nadir levels. Longer TTN is strongly associated with a low risk of disease progression, and the cutoff value of TTN could be inversely correlated with disease progression.