The purpose of this study is to establish the recommended doses and further evaluate the safety and preliminary antitumor activity of M3554 in participants with soft tissue sarcoma (STS) and glioblastoma, IDH-wildtype.

Study details include:

Study Duration per participant: Approximately 4 months

Inclusion Criteria:

• Escalation A: participants with documented histopathological diagnosis of locally advanced or metastatic STS with unresectable disease that has progressed after at least one prior line of anthracycline-containing systemic therapy for the locally advanced/metastatic setting.

• Participants with resectable locally advanced or metastatic disease, who had surgery before study entry will be allowed in the trial if there is residual disease after surgery and if the surgery was performed at least 4 weeks before first dose of study intervention.

• Escalation B: participants with documented histopathological diagnosis of glioblastoma, IDH-wildtype, who have progressed after ONLY one prior line of therapy (including radiotherapy +/- temozolomide, depending on the O^6-methylguanine-DNA methyltransferase [MGMT] status) and relapsing at least 3 months after the end of the radiotherapy treatment.

• Eastern Cooperative Oncology Group Performance Status (ECOG PS) below or equal to 1

• Participants with adequate hematologic, hepatic and renal function as defined in protocol

• Other protocol defined inclusion criteria could apply

  • Exclusion Criteria:

• Participant has a history of malignancy other than STS or glioblastoma (depending on the escalation/expansion cohort) within 3 years before the date of enrollment (exceptions are squamous and basal cell carcinomas of the skin and carcinoma in situ of the cervix, benign prostate neoplasm/hypertropia, or malignancy that in the opinion of the Investigator, is considered cured with minimal risk of recurrence within 3 years).

• STS only: Participants with history of brain metastasis, leptomeningeal metastasis, or participants with spinal cord compression

• Other protocol defined exclusion criteria could apply

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