Inclusion Criteria:

          -  Histologically confirmed locally advanced or metastatic undifferentiated pleomorphic
             sarcoma (UPS) or grade ≥ 2 myxofibrosarcoma (MFS)

          -  Documented progression following systemic chemotherapy

          -  At least one measurable lesion

          -  Eastern Cooperative Oncology Group performance status of 0 or 1

          -  Adequate hematologic and organ function

        Exclusion Criteria:

          -  More than two prior lines of chemotherapy for UPS/MFS

          -  Prior immune checkpoint inhibitor or immunomodulatory therapy

          -  Active autoimmune disease that has required systemic treatment

          -  Major surgery within 4 weeks of dosing of investigational agent

          -  Active additional malignancy

          -  Pericardial effusion, pleural effusion, or ascites

          -  Central nervous system metastases and/or carcinomatous meningitis

          -  Active hepatitis or cirrhosis

          -  Interstitial lung disease

          -  Unwilling to apply highly effective contraception during the study

          -  Other concurrent severe and/or uncontrolled medical conditions that would, in the
             investigator's judgment, contraindicate patient participation in the clinical study