A Study to Investigate Sitravatinib as Monotherapy and in Combination With Tislelizumab in Participants With Unresectable Locally Advanced or Metastatic Hepatocellular Carcinoma or Gastric/Gastroesophageal Junction Cancer

Key Inclusion Criteria: * Histologically or cytologically confirmed, unresectable, locally advanced, or metastatic HCC/gastric cancer/GEJ cancer * Able to provide written informed consent and can understand and agree to comply with the requirements of the study and the schedule of assessments * Age ≥ 18 years on the day of signing the informed consent form (or the legal age of consent in the jurisdiction in which the study is taking place) * Adequate organ function * Females of childbearing potential must be willing to use a highly effective method of birth control for the duration of the study, and ≥ 120 days after the last dose of study drug(s), and have a negative serum pregnancy test ≤ 7 days of first dose of study drug(s) * Nonsterile males must be willing to use a highly effective method of birth control for the duration of the study and for ≥ 120 days after the last dose of study drug(s) * Failed current standard-of-care treatment, or standard-of-care treatment is considered not appropriate at present Key Exclusion Criteria: * Active leptomeningeal disease or uncontrolled brain metastasis * Active autoimmune diseases or history of autoimmune diseases that may relapse * Any active malignancy ≤ 2 years before first dose of study drug(s) * History of interstitial lung disease, noninfectious pneumonitis or uncontrolled diseases including pulmonary fibrosis or acute lung diseases * Severe chronic or active infections (including tuberculosis infection) requiring systemic antibacterial, antifungal, or antiviral therapy within 14 days prior to first dose of study drug(s) * Known history of human immunodeficiency virus (HIV) infection * Untreated chronic hepatitis B or chronic hepatitis B virus (HBV) carriers. * Any major surgical procedure requiring general anesthesia ≤ 28 days before the first dose of study drug(s) * Prior allogeneic stem cell transplantation or organ transplantation * Inadequately controlled hypertension (defined as systolic blood pressure \> 150 mmHg and/or diastolic blood pressure \> 100 mmHg) * Bleeding or thrombotic disorders or use of anticoagulants such as warfarin or similar agents requiring therapeutic international normalized ratio (INR) monitoring * Any systemic chemotherapy within 28 days of the first dose of study drug(s) or hormone therapy, targeted therapy, or any investigational therapies * Toxicities (as a result of prior anticancer therapy) that have not recovered to baseline or stabilized, except for adverse events not considered a likely safety risk (eg, alopecia, neuropathy, and specific laboratory abnormalities) * Inability to swallow capsules or disease significantly affecting gastrointestinal function * Pregnant or breastfeeding woman NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.