Enzalutamide (XTANDI) with androgen deprivation therapy (ADT) delays the development of metastatic disease in men with M0 castration-resistant prostate cancer (CRPC) compared with ADT alone, according to results from the randomized phase III PROSPER study.
Further, early data suggest a potential improvement in overall survival (OS) in enzalutamide-treated men relative to placebo, said Maha Hussain, MD, at the Genitourinary Cancers Symposium in San Francisco.
Nonmetastatic (M0) castration-resistant prostate cancer is an area of unmet need with no currently approved therapies.
“The development of metastases is very predictable in this group of patients and is associated with increasing baseline PSA and PSA doubling time of less than 10 months,” said Dr. Hussain, of the Robert H. Lurie Comprehensive Cancer Center at Northwestern University, Chicago. “Delaying time to all metastases, which is a very clinically relevant endpoint because that is the terminal phase of the disease, is important, with the potential to delay cancer-related morbidity, improve survivorship, and also prolong OS.”
Enzalutamide gained approval by the FDA because it significantly improved OS and radiographic progression-free survival (PFS) in men with chemotherapy-naïve metastatic CRPC in the PREVAIL study. Enzalutamide also was superior to bicalutamide (Casodex) in improving radiographic PFS in a subgroup of patients with chemotherapy-naïve M0 CRPC.
PROSPER included 1,401 patients with PSA doubling time ≤10 months who were randomly assigned 2:1 to receive enzalutamide, 160 mg/day, with ADT or placebo plus ADT. The median age was 74 years in the enzalutamide group and 73 years in the placebo arm. The median PSA doubling time was 3.8 and 3.6 months, respectively, in the two arms.
The primary outcome was metastases-free survival (MFS), defined as time from randomization to radiographic progression or death within 112 days of treatment discontinuation.
At the data cut-off of June 28, 2017, the median duration of therapy of therapy was 18.4 months for enzalutamide and 11.1 months for placebo.
“As of early February of this year, we had still 61% of patients on the enzalutamide arm and 28% are active on the placebo arm,” Dr. Hussain said.