A First-in-Human Study of BGB-C354 Alone and in Combination With Tislelizumab 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. Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1. 3. Participants with histologically or cytologically confirmed advanced, metastatic, or unresectable solid tumors, whose cancer is not amenable to therapy with curative intent: 4. ≥ 1 measurable lesion per RECIST v1.1. 5. Able to provide an archived tumor tissue sample. 6. Adequate organ function. 7. Females of childbearing potential must be willing to use a highly effective method of birth control for the duration of the study, and for ≥ 7 months after the last dose of study drug(s). 8. Nonsterile males must be willing to use a highly effective method of birth control for the duration of the study treatment period and for ≥ 4 months after the last dose of study drug(s). Exclusion Criteria: 1. Prior treatment with B7H3-targeted therapy. 2. For Part B and Phase 1b: Prior treatment with antibody drug conjugates (ADCs) with topoisomerase I inhibitor payload (for Phase 1b, unless otherwise specified for specific cohorts). 3. Participants with spinal cord compressions, active leptomeningeal disease or uncontrolled, or untreated brain metastasis 4. Any malignancy ≤ 2 years before the first dose of study treatment(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). 5. History of interstitial lung disease, ≥ Grade 2 noninfectious pneumonitis, oxygen saturation at rest \< 92%, or requirement for supplemental oxygen at baseline 6. Uncontrolled diabetes, or \> Grade 1 laboratory test abnormalities in potassium, sodium, or corrected calcium levels despite standard medical management ≤ 14 days before the first dose of study drug(s). 7. Infection (including tuberculosis infection) requiring systemic (oral or intravenous) antibacterial, antifungal, or antiviral therapy ≤ 14 days before the first dose of study treatment(s). Note: Other protocol defined Inclusion/Exclusion criteria may apply.