Inclusion Criteria

• Locally advanced, relapsed, or metastatic sarcoma with measurable tumor burden following therapy, as defined by RECIST v1.1; the total of all lesions must be ≤12 cm (for synovial sarcoma) or ≤15 cm (for myxoid/round cell liposarcoma)
• Tumor histology consistent with synovial sarcoma or MRCL.
• Tumor specimen positive for NY-ESO-1 expression by IHC.
• Inadequate response, relapse, and/or unacceptable toxicity with ≥ 1 prior systemic, surgical, or radiation cancer therapy
• Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1

Exclusion Criteria

• Investigational therapy within 4 weeks prior to CMB305 dosing
• Prior administration of other NY-ESO-1-targeting immunotherapeutics
• Prior treatment with CD137 agonists or immune checkpoint blockade therapies, including anti-CTLA-4, anti PD-1, and anti PD-L1 therapeutic antibodies, or any other antibody or drug targeting T-cell costimulation
• Treatment with systemic immunostimulatory agents (including but not limited to interleukin-2) within 4 weeks or five half-lives of the drug, whichever is shorter, prior to first dose
• Significant immunosuppression
• Other cancer therapies, including chemotherapy, radiation, biologics or kinase inhibitors within 3 weeks prior to the first scheduled dosing
• History of autoimmune disease, including but not limited to myasthenia gravis, myositis, autoimmune hepatitis, systemic lupus erythematosus, rheumatoid arthritis, inflammatory bowel disease, vascular thrombosis associated with antiphospholipid syndrome, Wegener's granulomatosis, Sjögren's syndrome, Guillain-Barré syndrome, multiple sclerosis, vasculitis, or glomerulonephritis
• History of idiopathic pulmonary fibrosis (including pneumonitis), drug-induced pneumonitis, organizing pneumonia (i.e., bronchiolitis obliterans, cryptogenic organizing pneumonia), risk of pulmonary toxicity, or evidence of active pneumonitis on screening chest CT scan
  • History of radiation pneumonitis in the radiation field (fibrosis) is permitted
• History of other cancer within 3 years
• Evidence of active tuberculosis or recent (<1 week prior to first scheduled dosing) clinically significant infection requiring systemic therapy
• Evidence of active hepatitis B (HepB), hepatitis C (HepC), or Human Immunodeficiency Virus (HIV) infection
• Known active or untreated central nervous system (CNS) metastases
• Pregnant, planning to become pregnant within 6 months of treatment, or nursing
• Known allergy(ies) to any component of CMB305, atezolizumab, or severe allergic reactions to monoclonal antibodies, fusion proteins, or CHO cell products