This is a First-in-Human, Phase 1, Dose-Escalation and Dose-Expansion study of BH3120, as a single agent and in combination with pembrolizumab, to assess safety, tolerability, MTD, RP2D, PK, and efficacy in patients with advanced or metastatic solid tumors. Dose-Escalation part is planned to establish the MTD or RD for Dose-Expansion part, while Dose-Expansion part is designed to assess potential efficacy of BH3120, as a single agent and in combination with pembrolizumab, when administered at the RD to subjects in indication-specific expansion cohorts.

Key Inclusion Criteria:

• Have a Histologically or cytologically confirmed non-CNS solid tumor that is metastatic or unresectable and for whom there is no available standard therapy.
• PD-L1 positive expression (Tumor Proportion Score ≥1% or Combined Positive Score ≥1).
• Have at least one lesion, not previously irradiated that can be accurately measured per RECIST version 1.1.
• Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.
• Age of 18 years or older (or country's legal age of majority if the legal age was >18 years)
• Adequate Hematologic and liver function.

Key Exclusion Criteria:

• Has received prior therapy with an anti-4-1BB(CD137) agent.
• Known active CNS metastases and/or carcinomatous meningitis.
• Known additional malignancy that is progressing or has required active treatment.
• History of chronic liver disease or evidence of hepatic cirrhosis.
• History of severe toxicities associated with a prior immunotherapy.
• Has ongoing or suspected autoimmune disease.
• Known active and clinically significant bacterial, fungal or viral infection including known human immunodeficiency virus (HIV) or acquired immunodeficiency syndrome (AIDS)-related illness, immunocompromised patients.