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Enzalutamide Receives Priority Review for Hormone-Sensitive Prostate Cancer

On August 21, an application for the androgen receptor inhibitor enzalutamide was granted priority review by the United States Food and Drug Administration (FDA). Enzalutamide is currently approved for treatment of both nonmetastatic and metastatic castration-resistant prostate cancer (mCRPC). This new application adds an indication for enzalutamide as a treatment for patients with metastatic hormone-sensitive prostate cancer (mHSPC). The approval is based on results from the phase III ARCHES trial. In this study, the combination of enzalutamide with androgen deprivation therapy (ADT) in mHSPC resulted in significant improvements in radiographic progression-free survival (PFS) compared with ADT alone (hazard ratio 0.39; P <.001). The addition of enzalutamide to ADT also resulted in significant improvements in prostate-specific antigen (PSA) progression, symptomatic skeletal events, and pain progression. Similar results were also observed in the phase III ENZAMET trial, where the combination of enzalutamide and ADT resulted in significant improvements in overall survival, PSA PFS, and clinical PFS. In both trials, the toxicity profile of enzalutamide was favorable and consistent with known safety of this agent in CRPC.

High Altitude: If approved, enzalutamide will join abiraterone and docetaxel as mCRPC treatments that have demonstrated efficacy in the setting of mHSPC. As these mCRPC treatments move to earlier stages of disease, treating CRPC might become more complex with a growing need for new treatment options. Most patients progressing on enzalutamide or abiraterone in the HSPC setting will respond poorly to further androgen inhibition, and novel, effective treatment options will be needed. Further, deciding whether to use abiraterone, enzalutamide, or docetaxel first in mHSPC continues to be investigated. Development of novel treatment options along with identification of biomarkers for sensitivity to androgen inhibition have become the major focus of research moving forward.

Ground Level: While most community oncologists are familiar with enzalutamide as a treatment for mCRPC, additional education will be necessary for proper use of this agent in patients with mHSPC. Along with docetaxel and abiraterone, approval of enzalutamide means there will be 3 agents available for use in combination with ADT. Community oncologists will need answers to complicated questions, including sequencing of these therapies and how their selection affects mCRPC treatment.