ASCO 2017: Phase II study of bipolar androgen therapy (BAT) in men with metastatic castration-resistant prostate cancer (mCRPC) and progression on enzalutamide (enza)

Chicago, IL ( Dr. Teply and colleagues presented results of their phase II trial assessing bipolar androgen therapy (BAT) in men with metastatic castration resistant prostate cancer (mCRPC) after progression on enzalutamide at the 2017 ASCO annual meeting in Chicago. Androgen receptor overexpression is an adaptive resistance mechanism in mCRPC. Interestingly, high dose testosterone may induce tumor response and restore normal androgen receptor expression in this setting. The objective of this study was to assess responses to BAT among men who had previously progressed on enzalutamide, as well as assess response to an enzalutamide re-challenge after BAT administration.

Inclusion criteria for this study included minimally symptomatic men with mCRPC with progression on enzalutamide. These patients then received testosterone cypionate 400 mg IM every 28-days with continued gonadal suppression until disease progression. Follow-up included PSA with every 28-day cycle of testosterone and CT and bone scans every 3 testosterone cycles. Following progression on BAT, patients were then re-challenged with enzalutamide. The co-primary endpoints were >50% PSA response to BAT and >50% PSA response to enzalutamide re-challenge. Secondary endpoints were (i) safety, (ii) objective response, (iii) progression-free survival (PFS), and (iv) effect on circulating tumor cell-based androgen receptor and AR-V7 expression. The null hypothesis was a >50% reduction rate of 5% for both endpoints, with the alternative hypotheses of 20% to BAT and 25% to enzalutamide re-challenge. For a power of 90% for BAT and 83% for enzalutamide re-challenge, with an overall type 1 error of 0.1, 30 patients were required for this study. Between 2014-2016, 30 patients were recruited with no dose limiting toxicities and only two patients experiencing transient pain flares with BAT administration. There were three Grade 3-4 adverse events that may have been secondary to BAT, including pulmonary embolism, NSTEMI and urinary obstruction. Thirty-percent of men achieved a >50% PSA reduction with BAT and 36% of men with measurable disease had an objective response by RECIST 1.1. Twenty-one patients proceeded to enzalutamide re-challenge, which resulted in 15 patients experiencing >50% PSA reduction, with a PFS of 4.8 months. Finally, 1/3 of AR-V7+ patients responded to BAT and all had decreased AR-V7/AR ratios after 3 cycles.

In conclusion, this is important preliminary data suggesting that BAT may have a role in PFS among men with mCRPC progressing on enzalutamide. There is an ongoing randomized controlled trial (NCT02286921) comparing BAT to enzalutamide for men with mCRPC – we eagerly await the results of this important trial.
Clinical trial: NCT02090114

Presented By: Benjamin A. Teply, The Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins University, Baltimore, MD, USA

Co-Authors: Hao Wang, Rana Sullivan, Irina Rifkind, Ashley Bruns, Morgan Decarli, Victoria J. Sinibaldi, Caroline F. Pratz, Jun Luo, Michael Anthony Carducci, Channing Judith Paller, Emmanuel S. Antonarakis, Mario A. Eisenberger, Samuel R. Denmeade

Written By: Zachary Klaassen, MD, Urologic Oncology Fellow, University of Toronto, Princess Margaret Cancer Centre
Twitter: @zklaassen_md

at the 2017 ASCO Annual Meeting - June 2 - 6, 2017 – Chicago, Illinois, USA