Clinical Characterization of Low Prostate-specific Antigen on Prognosis in Patients With Metastatic Castration-naive Prostate Cancer.

INTRODUCTION: This study aimed to investigate the effect of low prostate-specific antigen (PSA) on prognosis, as the association of initial PSA level with prognosis in patients with metastatic castration-naive prostate cancer (mCNPC) remains unclear. PATIENTS AND METHODS: We evaluated 575 patients with mCNPC from 10 hospitals. Patients were stratified into 2 groups according to their initial PSA: PSA < 100 and PSA ≥ 100 groups. We compared castration-resistant prostate cancer (CRPC)-free survival, overall survival (OS), and OS from the CRPC diagnosis between the groups. Multivariate Cox regression analysis was performed to evaluate the effect of initial PSA level on prognosis. RESULTS: Of the 575 patients, 196 (34%) patients belonged to the PSA < 100 group. No significant difference was found in patients' backgrounds except for PSA, the extent of disease, and high tumor burden between the groups. CRPC-free survival was significantly shorter in the PSA ≥ 100 group than in the PSA < 100 group. However, the OS after CRPC diagnosis was significantly shorter in the PSA < 100 group than that of the PSA ≥ 100 group. Multivariate analyses showed that PSA < 100 ng/mL was an independent factor for OS after CRPC, whereas no significant association was observed in the CRPC-free survival and OS. CONCLUSIONS: A significant effect of initial PSA < 100 ng/mL on OS after CRPC was observed. PSA < 100 ng/mL might be a poor prognostic factor in patients with mCNPC after CRPC.