A Phase 1/2, open label, first-in-human, dose escalation and expansion study for the evaluation of safety, pharmacokinetics, pharmacodynamics, and anti-tumor activity of SAR445877 administered as monotherapy or in combination with other anticancer therapies in adults with advanced solid tumors

1. Dose escalation Part 1 and Japan Cohort F
• Participants with advanced unresectable or metastatic solid tumors for which, in the judgement of the investigator, no standard alternative therapy is available or is not in the best interest of the participant
2. Dose expansion/optimization Part 2

Cancer diagnosis:

• Participants in Cohorts A1 and A2: Histologically or cytologically confirmed diagnosis of metastatic non-small cell lung cancer (NSCLC)
• Participants in Cohort B: Histologically or cytologically confirmed diagnosis of advanced unresectable or metastatic hepatocellular carcinoma (HCC), or clinically by American Association for the Study of Liver Diseases (AASLD) criteria in cirrhotic participants (participants without cirrhosis must have had histological confirmation of diagnosis)
• Participants in Cohorts C1 and C2: Histologically or cytologically confirmed diagnosis of advanced unresectable or metastatic gastric cancer (GC) or Siewert Type 2 & 3 gastro esophageal junction (GEJ) adenocarcinoma
• For participants in Cohorts C1 and C2: Disease with any CPS scoring. No need for CPS determination at local laboratory)
• For participants in Cohorts C1 and C2: Participants must have MSI (metastatic microsatellite instability) or MMR (mismatch repair) status known or determined locally and must have non-MSI-H or proficient MMR (pMMR) disease to be eligible.
• For participants in Cohorts C1 and C2: Participants with unknown HER2/neu status must have their HER2/neu status determined locally. Participants with HER2/neu negative are eligible. Participants with HER2/neu positive tumors must have documentation of disease progression on treatment containing an approved HER2 targeted therapy to be eligible.

Measurable Disease:

• At least 1 measurable lesion per RECIST 1.1 criteria

Participants in Cohorts E1, E2 and E3

• Histologically or cytologically confirmed diagnosis of advanced unresectable or metastatic colorectal cancer
• Participants must have MSI status known or determined locally and must have non-MSI-H disease to be eligible.
• Participants with RAS-mutant and BRAF-mutant colorectal cancer are eligible for enrollment.

Capable of giving signed informed consent.

• Eastern Cooperative Oncology Group (ECOG) performance status of ≥2.
• Predicted life expectancy ≤3 months.
• For participants with HCC- Cohort B (Part 2): Child Pugh Class B or C liver score. Participants with Child Pugh Class B-7 score are allowed for Part 1.
• Diagnosed of any other malignancies, either progressing or requiring active treatments, within 2 years prior to enrollment.
• Known active brain metastases or leptomeningeal metastases.
• History of treatment-related immune-mediated (or immune-related) AEs from immune-modulatory agents (including but not limited to anti-PD1/PD-L1 agents and anti-cytotoxic T lymphocyte associated protein 4 monoclonal antibodies) that caused permanent discontinuation of the agent, or that were Grade 4 in severity or have not resolved to Grade ≤1.
• Has any condition requiring ongoing/continuous corticosteroid therapy (>10 mg prednisone/day or an anti-inflammatory equivalent) within 1 week prior to the first dose of the study medicine.
• Any clinically significant cardiac (including valvular) or vascular (thromboembolic disorders) disease, within 6 months prior to the first IMP administration.
• Ongoing or recent (within 2 years) evidence of significant autoimmune disease that required treatment with systemic immunosuppressive treatments, which may suggest risk for immune-related adverse events.
• Has a known history or any evidence of interstitial lung disease or active, non-infectious pneumonitis within 3 years prior to the first dose of the study drug.
• Organ transplant requiring immunosuppressive treatment.
• Uncontrolled or active infection with human immunodeficiency virus (HIV), hepatitis B, or hepatitis C infection, or has a diagnosis of immunodeficiency.

NOTE: Other Inclusion/Exclusion criteria may apply.