Last week, the United States Food and Drug Administration (US FDA) expanded the indications for Xtandi (enzalutamide). Previously, Xtandi was approved for use by men with castration-resistant, metastatic prostate cancer (prostate cancer that does not respond to decreasing testosterone levels in the body, and that has spread to other parts of the body). After the FDA’s new approval, Xtandi is now also indicated for use by individuals with non-metastatic castration-resistant prostate cancer (NM-CRPC). Although the castration-resistant indication has not changed, it has been deemed safe and effective for individuals with both metastatic and non-metastatic forms of CRPC to take Xtandi.1
What is Xtandi?
Xtandi is a nonsteroidal antiandrogen (NSAA) that inhibits the androgen receptor in the body, potentially reducing or blocking the body’s ability to respond to testosterone. Androgens, like testosterone may fuel the growth of prostate cancer tumors. Blocking the body’s ability to respond to testosterone, as opposed to just reducing its amount, may decrease prostate cancer tumor growth. Xtandi is often used alongside other forms of androgen deprivation therapy such as orchiectomy (surgical castration), or gonadotropin-releasing hormone agonists (called GnRH or LHRH agonists).2
Positive outcomes from clinical trials
The FDA made its approval based on data from the PROSPER trial, a Phase 3, randomized, placebo-controlled, double-blind study that took place across multiple sites and included over 1,400 individuals with NM-CRPC. These individuals had prostate cancer that had progressed even when taking androgen deprivation therapy, but that had not yet spread to other parts of the body. Individuals were given either Xtandi with androgen deprivation therapy or placebo with androgen deprivation therapy.1,3
The primary endpoint of the study was to assess metastasis-free survival (MFS). MFS is defined as the amount of time passed until metastasis is detected or until death. Other endpoints studied were time until PSA progression, overall survival, and time until the first use of an antineoplastic therapy. Overall, a significant improvement in MFS was found for individuals taking Xtandi with androgen deprivation therapy when compared to placebo with androgen deprivation therapy. Those taking Xtandi experienced a median MFS of 36.6 months, while those on placebo had a median MFS of 14.7 months. Additionally, individuals taking Xtandi experienced a 93 percent reduction in relative risk of PSA progression when compared to their placebo-receiving counterparts, delaying PSA progression by 33.3 months on average, as opposed to 3.9 months for those receiving placebo. Xtandi was also found to delay the time to first use of a new antineoplastic therapy when compared to the placebo group.1,3
The dosage of Xtandi recommended for NM-CRPC is four 40 mg capsules once a day, for a total of 160 mg daily. The most common side effects of Xtandi in the PROSPER trial were nausea, dizziness, falls, hot flush, fatigue, and hypertension.1
FDA Approved Enzalutamide for Castration-Resistant Prostate Cancer. US Food and Drug Administration. https://www.fda.gov/Drugs/InformationOnDrugs/ApprovedDrugs/ucm613543.htm?utm_campaign=Oncology%207/13/2018%20&utm_medium=email&utm_source=Eloqua&elqTrackId=a5307d59358649b9aee461fb56e8ee55&elq=18bfc6dc0ee143f29ae5abcee90f515a&elqaid=4257&elqat=1&elqCampaignId=3346. Published July 13, 2018. Accessed July 17, 2018.
Xtandi Prescribing Information. Astellas Pharma. Available from: https://www.astellas.us/docs/us/12A005-ENZ-WPI.pdf?v=1. Published July 2018. Accessed July 17, 2018.
Phase 3 PROSPER Trial Shows Xtandi (Enzalutamide) Significantly Reduced the Risk of Metastasis or Death by 71 Percent in Men with Non-Metastatic Castration-Resistant Prostate Cancer. Pfizer Inc. https://www.pfizer.com/news/press-release/press-release-detail/phase_3_prosper_trial_shows_xtandi_enzalutamide_significantly_reduced_the_risk_of_metastasis_or_death_by_71_percent_in_men_with_non_metastatic_castration_resistant_prostate_cancer. Published February 5, 2018. Accessed July 17, 2018.