The study consists of two phases:
1. Phase I:
The Phase I part includes two groups: Part 1 will assess the combination of tulmimetostat with darolutamide (Group A), and Part 2 will assess tulmimetostat with abiraterone (Group B). The primary objective of Phase I is to determine the recommended dose escalations (RDEs) for each combination, with enrollment using a staggered approach between groups.
Participants in both groups will continue androgen deprivation therapy (ADT) to maintain castrate testosterone levels (<50 ng/dL or <1.7 nmol/L), as determined by the investigator based on local guidelines. In Group B, abiraterone will be administered with an oral corticosteroid (prednisone or prednisolone) per local prescribing information.
2. Phase II:
Phase II is a randomized, open-label, multicenter dose-expansion study to further evaluate the recommended dose(s) of tulmimetostat in combination with darolutamide and provide proof-of-concept for efficacy and safety. Participants will be randomized to receive tulmimetostat plus darolutamide or darolutamide alone.
Eligible participants include those with metastatic hormone-sensitive prostate cancer (mHSPC) who are either de novo or recurrent, without prior radioligand therapy, but who may have received prior taxane-based chemotherapy and/or androgen receptor pathway inhibitors (ARPIs), excluding darolutamide. The study evaluates tulmimetostat-based combinations as potential treatment options for men with mHSPC.
The study for each participant consists of a screening period, a study treatment period followed by a post treatment long-term follow-up.