Japanese company Astellas and US-headquartered Pfizer have announced final overall survival (OS) for Xtandi (enzalutamide) in non-metastatic castration-resistant prostate cancer (nmCRPC).

Xtandi is being studied in this patient group alongside androgen deprivation therapy (ADT) in the Phase III PROSPER trial. The drug demonstrated statistically significant improvement in OS – the key secondary endpoint in the study – compared to placebo plus ADT.

Detailed safety and efficacy results from the final PROPSER OS analysis will be shared at a later date. Other secondary endpoints in the study are time to prostate-specific antigen (PSA) progression and time to use antineoplastic therapy.

This announcement follows on from 2018 primary endpoint PROSPER results of metastasis-free survival. It was measured from the time that participants entered the trial to until their cancer was radiographically detected as having metastasised or they died within 112 days of treatment discontinuation. These results were presented at the Genitourinary Cancers Symposium, and then published in The New England Journal of Medicine .

Xtandi is an androgen receptor indicator, which was approved for nmCRPC in July 2018 by the US Food and Drug Administration (FDA). This made it the first FDA-approved drug for both nmCRPC and mCRPC; it was approved for the latter in 2012.

Prostate Cancer Foundation president and CEO Jonathan Simmons commented: “”With today’s approval, there is now a new option for men with non-metastatic CRPC, who are in between the failure of androgen deprivation therapy resulting in CRPC and the onset of metastatic disease.”

The drug is also approved for nmCRPC in Europe and Japan; it is currently under review in China.

CRPC is a subset of men whose PC progresses although they are taking ADT and have castrate levels of testosterone. nmCRPC means the cancer has not spread to other parts of the body and there is a rising PSA level; many nmCRPC patients with a rising PSA level quickly develop mCRPC.

The drug has also been approved for metastatic castration-sensitive prostate cancer, and is being studied in the Phase III ARCHES trial in patients with metastatic hormone-sensitive, but not yet resistant, prostate cancer.

Astellas and Pfizer initiated their global agreed to develop and commercialise enzalutamide in October 2009. They jointly commercialise Xtandi in the US, while Astellas alone commercialises the drug outside of the US.