Enzalutamide Approved by FDA for Nonmetastatic Castration-Resistant Prostate Cancer

According to Pfizer and Astellas, the codevelopers of enzalutamide (Xtandi), the agent has been approved by the FDA for the treatment of patients with nonmetastatic castration-resistant prostate cancer (CRPC).

Based on results from the phase III PROSPER trial, the antiandrogen agent in combination with androgen deprivation therapy (ADT) reduced the risk of metastases or death by 71% for patients with nonmetastatic CRPC, compared to ADT alone.

PROSPER, a double-blind study, demonstrated the median metastasis-free survival (MFS) was 36.6 months with enzalutamide plus ADT versus 14.7 months with ADT alone (HR, 0.29; 95% CI, 0.24-0.35;P<.0001).

"With today&rsquo;s approval, there is now a new option for men with nonmetastatic CRPC, who are in between the failure of androgen deprivation therapy resulting in CRPC and the onset of metastatic disease,&rdquo; Jonathan Simons, MD, Prostate Cancer Foundation President and CEO, said in a statement. &ldquo;As a foundation that drives research aimed at improving patient outcomes, it is exciting to see approvals like this, which are vital to help address unmet patient needs.&rdquo;

In the phase III PROSPER trial, 1401 patients with asymptomatic M0 CRPC were randomized to receive ADT plus enzalutamide at 160 mg daily (n = 933) or a matching sugar pill placebo (n = 468). ADT consisted of a gonadotropin-releasing hormone agonist/antagonist. All patients in the study had testosterone levels of &le;50 ng/dL, a prostate-specific antigen (PSA) doubling time of &le;10 months, and a PSA of &ge; 2 ng/mL.

The primary endpoint of the study was MFS within 112 days of treatment discontinuation. Secondary endpoints of the study focused on PSA, time to next antineoplastic therapy, and overall survival (OS). Median duration of treatment with enzalutamide was 18.4 months compared with 11.1 months for the placebo group.

There was a 93% reduction in the risk of PSA progression in the enzalutamide arm compared with ADT alone (HR, 0.07; 95% CI, 0.05-0.08;P<.0001). The median time to PSA progression in the enzalutamide group was 37.2 months compared with 3.9 months for ADT alone.

The time to next antineoplastic therapy was extended by a median of 21.9 months with enzalutamide versus ADT alone. Men enrolled in the enzalutamide arm required a new therapy after a median of 39.6 months compared with 17.7 months in the placebo group, representing a 79% reduction in the risk of requiring a new therapy (HR, 0.21; 95% CI, 0.17-0.26;P&nbsp;<.0001).

The initial results from the PROSPER trial were available 2 years earlier than estimates, which predicted data maturation in 2020. At the time of the analysis, OS data were not yet mature, with medians unavailable for each arm. At this early stage, however, there was a trend toward improvement in OS with the addition of enzalutamide (HR, 0.80; 95% CI, 0.06-1.09;P= .1519).

There were significantly more adverse events (AEs) in the enzalutamide group compared with placebo (87% vs 77%). Grade &ge;3 AEs were experienced by 31% of men in the enzalutamide arm compared with 23% of those in the placebo group. The grade &ge;3 AEs that were more common in the enzalutamide group versus placebo, respectively, were hypertension (5% vs 2%) and fatigue (3% vs 1%).

AEs led to treatment discontinuation for 9% of patients in the enzalutamide arm compared with 6% in the placebo group. Five percent of patients in the enzalutamide arm experienced major cardiovascular events compared with 3% in the ADT alone arm. There were 3 seizures reported in the enzalutamide arm compared with none in the placebo group.

Reference:

Hussain M, Fizazi K, Saad F, et al. PROSPER: A phase 3, randomized, double-blind, placebo (PBO)-controlled study of enzalutamide (ENZA) in men with nonmetastatic castration-resistant prostate cancer (M0 CRPC).J Clin Oncol.2018;36 (suppl 6S; abstr 3).

The FDA initially approved enzalutamide in 2012 as a treatment for men with metastatic CRPC following docetaxel. This approval was expanded in 2014 to include treatment with the antiandrogen agent prior to chemotherapy.