A Phase Ib/II Study to Evaluate Safety and Efficacy of Bexmarilimab in Combination With Doxorubicin in Metastatic Soft-tissue Sarcoma.

This trial will Study a type of sarcoma defined metastatic soft-tissue sarcoma (STS). Participants will be treated with bexmarilimab, a CLEVER-1 antibody plus doxorubicin, a chemotherapy. The main purpose of the Study is to analyze the safety (to find out how safe or toxic a treatment is to appropriately manage the risks) and efficacy (to find out how effective a treatment is) of bexmarilimab combined with doxorubicin in participants who have STS.

Inclusion Criteria: 1. Participant, or legal representative (if applicable), must be capable to understand the purpose of the Study and have signed written informed consent form (ICF) prior to beginning specific protocol procedures. 2. Female or male participants ≥ 18 years of age at the time of signing ICF. 3. For phase Ib (dose escalation): * Histologically documented metastatic STS with no more than 3 lines of treatment. * Participant has not received doxorubicin, but doxorubicin could be indicated for metastatic disease as per institutional guidelines. For phase Ib (dose expansion) and for phase II: • Metastatic STS with any of the following histologies: undifferentiated pleomorphic sarcoma (UPS), myxofibrosarcoma (MFS), dedifferentiated liposarcoma (DDLPS), myxoid liposarcoma (MLPS), leiomiosarcoma (LMS) with no prior treatment in the advanced setting. Capped to 33% of participants with UPS/MFS, 33% of participants with DDLPS/MLPS, and 33% of participants with LMS. 4. Measurable disease according to RECIST v.1.1. 5. Participant has adequate bone marrow, liver, and renal function: * Hematological (without platelet, red blood cell transfusion, and/or granulocyte colony-stimulating factor support within 7 days before first Study treatment dose): Absolute neutrophil count (ANC) ≥ 1,000/mm3, platelet count ≥ 100 × 109/L, and hemoglobin ≥ 9.0 g/dL. * Hepatic: Serum albumin ≥ 2.5 g/dL; total bilirubin ≤ 1.5 times upper limit of normal (ULN) (≤ 3 ×ULN if Gilbert's syndrome); alkaline phosphatase (ALP) ≤ 2.5 ×ULN; aspartate transaminase (AST) and alanine transaminase (ALT) ≤ 2.5 ×ULN in participants with no liver metastasis and 5.0 ×ULN in participants with liver metastasis; partial thromboplastin \[PT\]-INR/activated partial thromboplastin time \[PTT\] \ 470 ms based on average of the screening triplicate 12-lead ECG. * Congenital long QT syndrome, family history of long QT syndrome, or unexplained sudden death under 40 years of age in first-degree relatives. 13. Participants with a history of chronic ulcers or clinically relevant liver disease leading to Child Pugh Score C or higher. If the history of abnormal liver function is related to previous hematologic malignancy or it's treatment, the participant may be enrolled after discussing with the Medical Monitor. 14. Pregnant or lactating women or participants not willing to apply highly effective contraception as defined in the protocol. 15. Any serious medical condition or abnormality in clinical laboratory tests that, in the investigator's judgment, precludes the participant's safe participation in and completion of the Study. 16. Current known infection with hepatitis B virus (HBV), or hepatitis C virus (HCV). Participants with past HBV infection or resolved HBV infection (defined as having a negative hepatitis B surface antigen \[HBsAg\] test and a positive hepatitis B core antibody \[HBcAb\] test, accompanied by a negative HBV DNA test) are eligible. Participants positive for HCV antibody are eligible only if polymerase chain reaction (PCR) is negative for HCV RNA. 17. Has active primary immunodeficiency, known human immunodeficiency virus (HIV) infection with positive viral load. Note: HIV-infected participants on effective anti-retroviral therapy with undetectable viral load are eligible for inclusion, provided their therapy does not include CYP3A4 inhibitors or inducers (such as nevirapine or atazanavir). 18. Other active uncontrolled infection at the time of enrollment. 19. Receipt of live or attenuated vaccine within 30 days prior to the first dose of Study treatment. 20. A history of uncontrolled seizures, central nervous system (CNS) disorders, or serious and/or unstable pre-existing psychiatric disability judged by the investigator to be clinically significant and adversely affecting compliance to Study drugs or interfering with participant safety. 21. Known substance abuse or any other concurrent severe and/or uncontrolled medical condition that would, in the investigator's judgment, contraindicate participant participation. 22. Inability or unwillingness to comply with the requirements of the protocol in the opinion of the investigator.