A Clinical Trial to Assess COM503 in Participants With Advanced Solid Malignancies

Inclusion Criteria: * Participants with histologically/cytologically confirmed advanced recurrent or metastatic solid tumor malignancy * Part 1 (dose escalation): Participants must have had disease progression on or following all available standard of care (SOC) therapies known to confer clinical benefit. * Part 2 (dose expansion): Participants may be enrolled following disease progression that has progressed after at least 1 available standard therapy; or for whom standard therapy has proven to be ineffective or intolerable or is considered inappropriate; or for whom a clinical trial of an investigational agent is a recognized SOC. * Participants must have a solid tumor measurable by computed tomography (CT) or magnetic resonance imaging (MRI) as per Response Evaluation Criteria in Solid Tumors version 1.1 (RECIST 1.1) criteria by investigator assessment Exclusion Criteria: * History of another malignancy within 2 years prior to the first trial intervention administration (unless the malignancy was treated with curative intent with low risk of recurrence \[e.g., nonmelanoma skin cancer, histologically confirmed complete excision of carcinoma in situ, or similar\] which are allowed to enroll). * Therapy with Immunosuppressive doses of systemic medications, such as steroids (doses \>10 mg/day prednisone or equivalent daily) within 2 weeks before trial intervention administration * Have known active central nervous system (CNS) metastases and/or leptomeningeal disease (LMD). * Active and clinically relevant bacterial, fungal, or viral infection that is not controlled or requires systemic antibiotics, antifungals, or antivirals, respectively. * Ascites or pleural effusion that is symptomatic and/or requiring drainage within 2 weeks prior to the first trial intervention administration. * Have active hepatitis B virus (HBV) or hepatitis C virus (HCV), or participants with human immunodeficiency virus (HIV). * Any medical condition that, in the investigator's or sponsor's opinion, poses an undue risk to the participant's participation in the trial.