Pfizer and Astellas Pharma have reported positive results from the Phase III PROSPER clinical trial of Xtandi (enzalutamide) in patients with non-metastatic castration-resistant prostate cancer (nmCRPC).

Xtandi is an androgen receptor inhibitor approved to treat castration-resistant prostate cancer (CRPC) and metastatic castration-sensitive prostate cancer (mCSPC).

The randomised, double-blind, placebo-controlled, multi-national PROSPER study assessed a 160mg dose of the drug in combination with androgen deprivation therapy (ADT) in a total of around 1,400 nmCRPC patients in the US, Europe, Canada, South America and Asia-Pacific.

Patients whose prostate cancer had progressed without any symptoms and no previous or current evidence of metastatic disease participated in the trial.

The primary endpoint was metastasis-free survival (MFS), defined as the time from patients enrolling in the trial until their cancer was found to have metastasised, or until death within 112 days after treatment discontinuation.

Key secondary endpoints of the trial included overall survival (OS), time to prostate-specific antigen (PSA) progression, and time to first antineoplastic therapy use.

Final analysis of OS data revealed a statistically significant improvement in the OS of patients treated with Xtandi plus ADT compared to the placebo and ADT combination.

Preliminary analysis showed an adverse event profile generally consistent with previous PROSPER data. The trial met its primary endpoint of MFS in 2018.

In 2018, the partners amended the protocols of the ARCHES and EMBARK registrational Phase III trials of Xtandi in hormone-sensitive prostate cancer (HSPC) patients.

The modifications revised the planned analyses of the primary and secondary endpoints of the trials, as well as their scheduled primary completion date.