A Study of Debio 0123 in Combination With Temozolomide in Adult Participants With Recurrent or Progressive Glioblastoma and of Debio 0123 in Combination With Temozolomide and Radiotherapy in Adult Participants With Newly Diagnosed Glioblastoma

The primary purpose of the Phase 1 (Dose Escalation) of this study is to identify the dose-limiting toxicities (DLTs) of Debio 0123 combined with temozolomide (TMZ) (Arm A) and with TMZ and radiotherapy (RT) (Arms B and C) and to characterize the safety and tolerability of these combinations in adult participants with glioblastoma (GBM). Arm B which was previously added to the protocol, has been permanently halted per the safety monitoring committees' decision on the safety findings of this arm. The primary purpose of Phase 1 (Dose expansion) of the study is to assess the doses studied under Phase 1 (Dose Escalation) Arm A and identify the recommended dose (RD) for further development. The Phase 2 will start once the RD Phase 1 has been defined. The primary objective of Phase 2 is to assess the efficacy of Debio 0123 at the RD for further development in combination with TMZ, compared to the standard of care (SOC) in adult participants with GBM.