NEW ORLEANS, LA USA (UroToday.com) - In today’s moderated poster session on advanced prostate cancer, Dr. Jonathan Hung and colleagues presented their work on the ability of primary hormonal therapy outcomes to predict subsequent response to abiraterone or enzalutamide in metastatic castration-resistant prostate cancer. Given that abiraterone acts by irreversibly inhibiting Cyp17A1 and that enzalutamide works as a high-affinity AR antagonist, the investigators hypothesized that there may be common mechanisms of resistance between initial ADT receipt and subsequent AR-targeted treatment. They performed a multi-center retrospective review to identify mCRPC patients who were ultimately treated with abiraterone or enzalutamide. They assessed use of primary ADT, PSA kinetics, biochemical PFS, and OS. Using regression analysis, they assessed the effects of primary therapy response on novel hormone therapy outcomes.
Fifty-one patients received abiraterone and 29 received enzalutamide, starting at a median age of 73.2 years. Median age at diagnosis was 64.6 years. Twenty-seven patients received docetaxel prior to novel ADT. On univariate anlaysis, time to progression (HR 0.88, p-0.032), PS 2 or 3 (HR 2.76, p=0.004), pre-treatment PSA (HR=1.32, p < 0.001), PSA nadir (HR=1.42, p < 0.001), time to nadir (HR=0.75, p < 0.001), and % PSA decline (HR=0.15, p < 0.001) were all associated with PFS. The authors found a median biochemical PFS of 1.9 years on primary ADT, with a median PSA decline of 99%. Time to PSA progression on primary ADT significantly impacted biochemical PFS on abiraterone or enzalutamide: those who progressed within one year had bPFS=3.4 months. Those who progressed after 1 year on primary ADT had bPFS = 7.6 months. Finally, those who progressed after 5 years had bPFS = 8.1 months.
The authors concluded that time to PSA progression on primary ADT had a significant effect on time to progression on abiraterone or enzalutamide. Those who had PSA progression within one year had significantly shorter bPFS on subsequent therapy. This data can be used to assist with guidance of treatment in mCRPC patients.
Presented by Jonathan Hung at the American Urological Association (AUA) Annual Meeting - May 15 - 19, 2015 - New Orleans, LA USA
Mayo Clinic, Rochester, MN USA
Reported by Nikhil Waingankar, medical writer for UroToday.com