ESSA Pharma Inc. announced the initiation of the Phase 2 portion of its Phase 1/2 study evaluating its lead candidate, masofaniten (formerly known as EPI-7386), a first-in-class N- terminal domain androgen receptor inhibitor, in combination with Astellas and Pfizer's antiandrogen enzalutamide in patients with metastatic castration-resistant prostate cancer ("mCRPC") naïve to second-generation antiandrogens. Updated results from the first four cohorts of patients from the Phase 1 dose escalation portion of the Phase 1/2 study have been selected for a poster presentation at the upcoming European Society of Medical Oncology ("ESMO") Congress taking place October 20-24, 2023, in Madrid, Spain. The Phase 2 dose expansion portion of the study is a two-arm, randomized, open-label study (NCT05075577) that will evaluate the safety, tolerability and preliminary efficacy of masofaniten, and is expected to enroll approximately 120 patients.

Patients will continue to receive androgen deprivation therapy and will be randomized 2:1 to receive either the combination of masofaniten (600mg twice-daily ("BID")) and enzalutamide (160mg once daily ("QD")) or enzalutamide (160mg QD) as a single agent. Patients may remain on study treatment as long as they are tolerating treatment without disease progression based on RECIST v1.1 and/or Prostate Cancer Clinical Trials Working Group 3 (PCWG3) criteria.