TulmiSTAR-02: A Phase I/II Open-label Study of Tulmimetostat in Combination With Darolutamide vs. Darolutamide, and Tulmimetostat With Abiraterone in Patients With Metastatic Hormone-sensitive Prostate Cancer (mHSPC)

The purpose of the study is to evaluate the safety, tolerability, and efficacy of the two different treatment combinations of tulmimetostat in participants with de novo or recurrent Metastatic Hormone-Sensitive Prostate Cancer (mHSPC).

The study consists of two phases: 1. 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 the groups. Participants in both Group A and Group B will continue androgen deprivation therapy (ADT) to maintain castrate testosterone levels (\< 50 ng/dL or \< 1.7 nmol/L), with the ADT modality determined by the investigator based on local guidelines. In Group B, abiraterone will be co-administered with an oral corticosteroid (prednisone or prednisolone) as per local prescribing information. 2. The Phase II part is a randomized, open-label, multicenter dose-expansion study designed to further evaluate the recommended dose(s) of tulmimetostat in combination with darolutamide and provide proof-of-concept for its efficacy and safety. Participants in Phase II will be randomized to receive either tulmimetostat plus darolutamide or darolutamide alone. Eligible participants include those with de novo or recurrent mHSPC who have not previously received prior radioligand therapy but may have prior exposure to taxane-based chemotherapy and/or androgen receptor pathway inhibitors (ARPI, excluding darolutamide). This study aims to explore tulmimetostat-based combinations as potential therapeutic 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.