Abstract
228 Background: 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 (pts); 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. Methods: 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 95% confidence interval (CI) of the NNT was derived based on the 95% CI of the event rate difference. Results: 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. Conclusions: This analysis 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.
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