Revisions to protocols of two trials of Xtandi in men with hormone-sensitive prostate cancer will accelerate timelines for anticipated primary completion . Pfizer + Astellas.

Pfizer Inc. and Astellas Pharma Inc. announced amendments to the protocols for two registrational Phase III trials, ARCHES and EMBARK, designed to evaluate the safety and efficacy of Xtandi (enzalutamide) in men with hormone-sensitive prostate cancer (HSPC). These amendments accelerate timelines for the anticipated primary completion dates of both trials.

ARCHES is a randomized Phase III study evaluating the efficacy and safety of enzalutamide plus androgen deprivation therapy (ADT) versus ADT alone in metastatic HSPC patients. The primary endpoint of the trial is radiographic progression-free survival (rPFS). Changes to the protocol include revision of the planned analyses of the primary and secondary endpoints. Enrollment was completed earlier this year. The companies now anticipate the primary completion date for the ARCHES clinical trial to be in late 2018. The previously expected primary completion date was April 2020.

Revisions were also made to the protocol for EMBARK, a randomized Phase III study of enzalutamide plus leuprolide, enzalutamide monotherapy, and leuprolide alone in men with high-risk non-metastatic HSPC. The primary endpoint of the trial is metastasis-free survival (MFS). The main purpose of the amendment is to revise the planned analyses of the primary and several secondary endpoints, which reduced the target sample size. Enrollment was completed earlier this year. With these changes, the estimated primary completion date for the EMBARK clinical trial is mid-2020. Previously, the expected primary completion date for EMBARK was March 2021.

Xtandi is approved by the FDA for the treatment of castration-resistant prostate cancer.

Comment: Non-metastatic prostate cancer indications give both Xtandi and Erleada from Johnson & Johnson an edge over Zytiga and future generics, since Zytiga is not approved for non-metastatic patients. Zytiga's label includes metastatic CRPC and metastatic high-risk castration-sensitive prostate cancer. The Zytiga exclusivity in the US is expected to expire this year.