Clinical Outcome and Prognostic Variables of Second-line Therapy for Patients With Castration-resistant Prostate Cancer After Failure of First-line Androgen Receptor Axis-targeted Therapy

Background: Despite the rapid introduction of androgen receptor-targeted agents (ARTA) into clinical practice for castration-resistant prostate cancer (CRPC), the optimal treatment strategy after first-line ARTA remains unclear. The object of this study was to clarify clinical outcomes of second-line therapy for CRPC after first-line ARTA. Patients and Methods: The medical records of 130 consecutive patients with CRPC with disease progression during first-line ARTA and who started second-line therapy at our Institution between 2014 and 2020 were analyzed. Results: A total of 130 patients with CRPC were identified. Ninety patients underwent ARTA-ARTA treatment, and 40 patients underwent ARTA-docetaxel treatment. The median observation period after second-line ARTA or docetaxel administration was 14.2 months. The prostate-specific antigen response rates overall, and after second-line ARTA, and docetaxel were 26.8%, 24.7%, and 31.6%, respectively. The median progression-free survival (PFS) and 1-and 2 -year PFS rates of second-line therapy were 7.9 months and 34.6% and 15.4%, respectively. The median overall survival (OS) and 1-and 2-year OS rates were 27.4 months and 81.8%, and 54.9%, respectively. Multivariate analyses for OS disclosed that a C-reactive protein over the upper limit of normal and time from first-line ARTA to progression under 12 months were associated with shorter OS. Prostate-specific antigen response, PFS and OS of second-line therapy were not significantly different between second-line ARTA and docetaxel. Conclusion: There was no significant difference in OS between ARTA-ARTA and ARTA-docetaxel groups in the present study, suggesting that second-line ARTA might be the preferred treatment after initial failure of ARTA.