ASCO GU 2018: Comparison of Enzalutamide and Bicalutamide in Patients with Non-metastatic Castration-resistant Prostate Cancer - STRIVE Study

San Francisco, CA ( Androgen receptor inhibitors enzalutamide (ENZA) and bicalutamide (BIC) are used to treat metastatic castration-resistant prostate cancer (mCRPC). The Phase 2 STRIVE trial included 35% non-metastatic (m0) and 65% metastatic CRPC patients. ENZA reduced the risk of progression or death among pts, with an adverse event profile consistent with previous trials. The objective of this analysis was to compare ENZA with BIC using the number needed to treat (NNT) to achieve one additional pt with m0CRPC, with either a progression-free survival (PFS) event, radiographic PFS (rPFS), or free of prostate-specific antigen (PSA) progression at 1 year and 2 years.

The 1- and 2-year event rates of PFS, rPFS, and progression-free PSA among pts treated with ENZA and BIC were obtained from the STRIVE trial report. The NNT was calculated as the reciprocal of the absolute risk reduction between ENZA and BIC at each time point. This represents the number of pts that need to be treated with ENZA, compared with BIC, to obtain one additional pt free of a clinical progression event. PFS was defined as the time from randomization to investigator-assessed radiographic (bone or soft tissue) progression, PSA progression, or death.

The NNT to achieve one additional pt with PFS at 1 year, comparing ENZA with BIC, was 2.2 (95% CI 1.7, 3.4), suggesting that treating three pts with ENZA instead of BIC would result in one additional pt free of progression or death at the end of 1 year. The NNT to achieve one additional pt with PFS at 2 years was also 2.2 (95% CI 1.5, 3.7). For rPFS, the NNTs comparing ENZA with BIC were 4.7 (95% CI 2.8, 14.6) and 3.0 (95% CI 2.0, 6.1) at 1 and 2 years, respectively. For progression-free PSA, the NNTs were 2.0 (95% CI 1.5, 2.8) and 2.0 (95% CI 1.4, 3.3) at 1 and 2 years, respectively.

This study supports the superior clinical benefit of ENZA versus BIC in men with m0CRPC. Pts treated with ENZA showed low NNT values across all clinical outcomes and time points. Clinical trial information: NCT01664923

Presented by: Raoul S Concepcion

Co Authors: Andrew J. Armstrong, Lawrence Ivan Karsh, Stefan Holmstrom, Cristina Ivanescu, Curtis Dunshee, Neeraj Agarwal, Michael O'Kelly, Shevani Naidoo, Carl A. Olsson, De Phung, Bohdana Ratitch, Fong Wang, Pavol Kral, David F. Penson; Vanderbilt University School of Medicine, Nashville, TN; Duke Cancer Institute, Duke University, Durham, NC; The Urology Center of Colorado, Denver, CO; Astellas Pharma Inc., Leiden, Netherlands; QuintilesIMS, Hoofddorp, Netherlands; Urological Associates of Southern Arizona P.C., Tucson, AZ; University of Utah Hunstman Cancer Institute, Salt Lake City, UT; QuintilesIMS, Dublin, Ireland; Astellas Pharma Inc., Chertsey, United Kingdom; Icahn School of Medicine at Mount Sinai, New York, NY; QuintilesIMS, Montreal, QC, Canada; Pfizer Inc., San Francisco, CA; QuintilesIMS, Bratislava, Slovakia; Vanderbilt University Medical Center, Nashville, TN

Written by: Hanan Goldberg, MD, Urologic Oncology Fellow (SUO), University of Toronto, Princess Margaret Cancer Centre, Twitter:@GoldbergHanan at the 2018 American Society of Clinical Oncology Genitourinary (ASCO GU) Cancers Symposium, February 8-10, 2018 - San Francisco, CA

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Enzalutamide Versus Bicalutamide in Castration-Resistant Prostate Cancer: The STRIVE Trial