On 13 July 2018, the US Food and Drug Administration (FDA) approved enzalutamide (XTANDI, Astellas Pharma US, Inc.), for patients with castration-resistant prostate cancer (CRPC). This approval broadens the indicated patient population to include patients with both non-metastatic CRPC and metastatic CRPC. Enzalutamide was previously approved for the treatment of patients with metastatic CRPC.
Approval in patients with non-metastatic CRPC was based on a randomised, multicentre clinical trial (PROSPER, NCT020032924). The study investigators hypothesized that enzalutamide, which prolongs overall survival among patients with metastatic CRPC would delay metastasis in men with non-metastatic CRPC and a rapidly rising PSA level.
In total 1,401 patients were randomised 2:1 to either enzalutamide 160 mg orally once daily or placebo orally once daily. Patients continued on gonadotropin-releasing hormone (GnRH) therapy or had prior bilateral orchiectomy.
The major efficacy outcome was metastasis-free survival, defined as the time from randomisation to loco-regional and/or distant radiographic progression (blinded independent central review), or death up to 112 days after treatment discontinuation without radiographic progression.
The trial demonstrated a statistically significant improvement in metastasis-free survival for patients receiving enzalutamide compared to those receiving placebo, with median metastasis-free survival of 36.6 and 14.7 months, respectively, hazard ratio (HR) 0.29; p < 0.0001.
The time to the first use of a subsequent antineoplastic therapy was longer with enzalutamide treatment than with placebo (39.6 vs. 17.7 months; HR 0.21; p < 0.001; such therapy was used in 15% vs. 48% of patients) as was the time to PSA progression (37.2 vs. 3.9 months; HR 0.07; p < 0.001; progression occurred in 22% vs. 69% of patients).
At the first interim analysis of overall survival, 103 patients (11%) receiving enzalutamide and 62 (13%) receiving placebo had died.
The study investigators published the PROSPER results on 28 June 2018 in The New England Journal of Medicine and concluded that among men with non-metastatic CRPC with a rapidly rising PSA level, enzalutamide treatment led to a clinically meaningful and significant 71% lower risk of metastasis or death than placebo.
Adverse events were consistent with the established safety profile of enzalutamide. The most common adverse reactions (≥10%) that occurred more frequently (≥2% over placebo) in the enzalutamide-treated patients in PROSPER were asthenia/fatigue, hot flush, hypertension, dizziness, nausea, and falls.
The recommended enzalutamide dose is 160 mg (four 40 mg capsules) administered orally once daily.
Full prescribing information for XTANDI is available here.
Healthcare professionals should report all serious adverse events suspected to be associated with the use of any medicine and device to FDA’s MedWatch Reporting System.