Presentation Authors: Maylynn Ding, Hamilton, Canada, Taehyoung Lee, New York, NY, Richard Di Lena*, Bobby Shayegan, Hamilton, Canada
Introduction: Androgen deprivation therapy (ADT) is a first-line treatment for advanced prostate cancer and an adjuvant for localized treatment of high-risk disease. There is debate regarding optimal medical castration levels. We aimed to determine if a lower testosterone level below the previously accepted castration level of < 50ng/dL has an impact on time to progression to castration-resistant prostate cancer (CRPC) in patients on continuous ADT.
Methods: This is a single-center, retrospective review of prospectively collected data on 156 consecutive patients who initiated continuous ADT at a tertiary centre from 2006 to 2017. Serum prostate-specific antigen (PSA) and testosterone levels were routinely assessed every 3 months after initiation of ADT. Patients were stratified based on absolute testosterone levels measured at 6 and 9 months following ADT initiation. Progression to CRPC was assessed using the Kaplan-Meier method and compared with the log-rank analysis.
Results: A total of 116 patients were included in the study. There were no baseline differences in age and pre-treatment PSA levels between groups. Median follow-up was 48 months (IQR: 30.5, 62.5). 41.4% of all patients were CRPC free at the date of last follow-up. In this study cohort, 71.6% of patients achieved a one-year mean testosterone level < 20ng/dL; 21.6% achieved 20-32ng/dL; 3.4% achieved 32-50 ng/dL; and 3.4% achieved â‰¥50ng/dL. Patients who achieved an absolute testosterone level of < 20ng/dL at 6 months had a significantly increased time to CRPC (log-rank p=0.025, median CRPC-free survival of 48 months [ < 20ng/dL] versus 24 months [â‰¥20 ng/dL]). Likewise, patients with a 9-month absolute testosterone level < 20ng/dL had a significantly increased time to CRPC (log-rank p=0.039, median CRPC-free survival 48 months [ < 20ng/dL] versus 20 months [â‰¥20ng/dL]).
Conclusions: Our study results support that strict testosterone control of < 20ng/dL in patients undergoing continuous ADT will lead to longer progression free survival. In this series, only a small proportion of patients had one-year mean testosterone levels of â‰¥32ng/dL (6.9%). A multi-centre prospective study is needed to validate these findings.