This is a first-in-human Phase I, open-label, dose-escalation and expansion study designed to evaluate the safety, tolerability, pharmacokinetics, immunogenicity, pharmacodynamic, and preliminary anti-tumor activity of RO7566802 as a single agent and in combination with atezolizumab in participants with locally advanced, recurrent, or metastatic incurable solid tumor malignancies. Participants will be enrolled in 2 stages: dose escalation and expansion.

Inclusion Criteria:

• Eastern Cooperative Oncology Group (ECOG) Performance Status of 0-1
• Life expectancy >=3 months, in the investigator's judgment
• Adequate hematologic and end-organ function
• Histologically confirmed locally advanced, recurrent, or metastatic incurable solid tumor malignancy that has progressed after available standard therapy; or for whom standard therapy has proven to be ineffective or intolerable or is considered inappropriate; or for whom a clinical trial of an investigational agent is a recognized standard of care
• Measurable disease per RECIST v1.1
• Tumor specimen availability, for certain cohorts

Exclusion Criteria:

• Any anti-cancer therapy, whether investigational or approved, including chemotherapy, hormonal therapy, or radiotherapy, within 3 weeks prior to Cycle 1 Day 1, with certain exceptions
• Active hepatitis B or C
• Active tuberculosis
• Positive test for human immunodeficiency virus (HIV) infection
• Administration of a live, attenuated vaccine (e.g., Flumist) within 4 weeks prior to RO7566802 infusion
• Symptomatic, untreated, or actively progressing central nervous system (CNS) metastases
• Active or history of autoimmune disease
• Prior allogeneic stem cell or organ transplantation
• Uncontrolled tumor-related pain
• Significant cardiovascular disease

Other protocol-defined inclusion/exclusion criteria may apply.