The phase 3 PROSPER trial evaluating Enzalutamide ( Xtandi ) plus androgen deprivation therapy ( ADT ) versus ADT alone in patients with non-metastatic ( M0 ) castration-resistant prostate cancer ( CRPC ) met its primary endpoint of improved metastasis-free survival ( MFS ). The preliminary safety analysis of the PROSPER trial appears consistent with the safety profile of Enzalutamide in previous clinical trials.

The phase 3 randomized, double-blind, placebo-controlled, multi-national trial enrolled approximately 1,400 patients with non-metastatic castration-resistant prostate cancer ( CRPC ) at sites in the United States, Canada, Europe, South America and the Asia Pacific region.
PROSPER enrolled patients with prostate cancer that had progressed, based on a rising prostate-specific antigen ( PSA ) level despite androgen deprivation therapy ( ADT ), but who had no symptoms with no prior or present evidence of metastatic disease.
The primary objective of the trial was metastasis-free survival. MFS is a measure of the amount of time that passes until a cancer can be radiographically detected as having metastasized, or spread, to other parts of the body.
The trial evaluated Enzalutamide at a dose of 160 mg taken orally once daily plus ADT, versus placebo plus ADT.

Enzalutamide is an androgen receptor inhibitor that blocks multiple steps in the androgen receptor signaling pathway within the tumor cell.
In preclinical studies, Enzalutamide has been shown to competitively inhibit androgen binding to androgen receptors, and inhibit androgen receptor nuclear translocation and interaction with DNA. The clinical significance of this mechanism of action is unknown.

According to the American Cancer Society ( ACS ), more than 161,000 men are estimated to be diagnosed with prostate cancer in 2017.
Castration-resistant prostate cancer refers to the subset of men whose prostate cancer progresses despite androgen deprivation therapy.
Non-metastatic CRPC means there is no clinically detectable evidence of the cancer spreading to other parts of the body, and there is a rising prostate-specific antigen ( PSA ) level.
Many men with non-metastatic CRPC will go on to develop metastatic CRPC.

Source: Pfizer & Astellas, 2017