Study of BG-T187 Alone and in Combination With Other Therapeutic Agents in Participants With Advanced Solid Tumors

Inclusion Criteria: 1. Able to provide a signed and dated written informed consent prior to any study-specific procedures, sampling, or data collection. 2. Participants must be ≥ 18 years of age or the legal age of consent in the jurisdiction in which the study is taking place. 3. Eastern Cooperative Oncology Group (ECOG) Performance Status ≤ 1. 4. Participants with selected histologically or cytologically confirmed advanced, metastatic, and unresectable solid tumors who have been previously treated, including but not limited to non-small cell lung cancer (NSCLC), colorectal cancer (CRC). 5. ≥ 1 measurable or nonmeasurable lesion as assessed by RECIST v1.1. for Phase 1a Part A; ≥ 1 measurable lesion per RECIST v1.1. for Phase 1a Part B and Phase 1b. 6. Adequate organ function. Exclusion Criteria: 1. Prior severe allergic reactions or hypersensitivity to the active ingredient and excipients of BG-T187 or other monoclonal antibodies. 2. Spinal cord compression, active leptomeningeal disease, or uncontrolled, untreated brain metastasis. 3. Any malignancy ≤ 3 years before the first dose of study drug(s) except for the specific cancer under investigation in this study and any locally recurring cancer that has been treated with curative intent (eg, resected basal or squamous cell skin cancer, superficial bladder cancer, or carcinoma in situ of the cervix or breast). 4. History of interstitial lung disease (ILD) or noninfectious pneumonitis requiring steroids or other immune suppressive agents ≤ 2 years before the first dose of the study drug, or with current ILD/noninfectious pneumonitis, or where suspected ILD/noninfectious pneumonitis cannot be ruled out by imaging during screening. 5. Uncontrollable pleural effusion, pericardial effusion, or ascites requiring frequent drainage (recurrence ≤14 days after intervention). 6. Active hepatitis C. 7. Infection (including tuberculosis infection, or other) requiring systemic (oral or intravenous) antibacterial, antifungal, or antiviral therapy ≤ 14 days before the first dose of study drug(s). Note: Other protocol defined Inclusion/Exclusion criteria may apply.