Key Inclusion Criteria:

          1. Histologically confirmed diagnosis of esophageal squamous cell carcinoma (ESCC)

          2. Tumor progression during or after first-line treatment for advanced unresectable /
             metastatic ESCC

          3. At least one measurable/evaluable lesion by RECIST v1.1

          4. Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 prior to
             randomization

          5. Adequate End organ function

        Key Exclusion Criteria:

          1. Receipt of 2 or more prior systemic treatments for advanced/metastatic unresectable
             ESCC

          2. History of gastrointestinal perforation and /or fistula or aorto-esophageal fistula
             within 6 months prior to randomization

          3. Apparent tumor invasion into organs located adjacent to the esophageal disease site
             (eg, aorta or respiratory tract) at an increased risk of fistula in the study
             treatment assessed by investigator

          4. Uncontrollable pleural effusion, pericardial effusion, or ascites requiring frequent
             drainage

          5. Received prior therapies targeting PD-1 or PD-L1

          6. Prior malignancy active within the previous 2 years (exceptions include the tumor
             under investigation in this trial, and locally recurring cancers that have undergone
             curative treatment, such as resected basal or squamous cell skin cancer, superficial
             bladder cancer or carcinoma in situ of the prostate, cervix or breast)

          7. Active brain or leptomeningeal metastasis.

          8. Has active autoimmune disease or history of autoimmune diseases at high risk for
             relapse

          9. Known history of, or any evidence of interstitial lung disease, non-infectious
             pneumonitis, pulmonary fibrosis diagnosed based on imaging or clinical findings, or
             uncontrolled systemic diseases, including diabetes, hypertension, acute lung diseases,
             etc

         10. Known history of Human Immunodeficiency Virus (HIV)

         11. Has cardiovascular risk factors

         12. Pregnant or breastfeeding woman.

        NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.