A study to evaluate the safety, pharmacokinetics and anti-tumor activity of RO7300490 as a single agent or in combination with atezolizumab. The study will consist of 3 parts: [Part 1] Dose-Escalation of RO7300490 as a single agent; [Part 2] Dose-Escalation of RO7300490 in combination with atezolizumab and [Part 3] Dose-Expansion of RO7300490 in combination with atezolizumab in selected cancer types.

Inclusion Criteria:

• Life expectancy of >= 12 weeks.
• Histologically confirmed diagnosis of locally advanced and/or metastatic solid tumors that are not amenable to standard therapy.
• Radiologically measurable disease as defined by Response Evaluation Criteria in Solid Tumors (RECIST) v1.1.
• Agreement to provide protocol-specific biopsy material.
• Adverse Events (AEs) from prior anti-cancer therapy resolved to Grade =<1.
• Adequate performance status and cardiovascular, hematological, liver, renal and coagulation function.
• For female participants of childbearing potential: agreement to remain abstinent (refrain from heterosexual intercourse), use contraceptive measures and refrain from donating eggs.
• For male participants: agreement to remain abstinent (refrain from heterosexual intercourse), use contraceptive measures and refrain from donating sperm.

Exclusion Criteria:

• Known central nervous system (CNS) primary tumors or metastases, including leptomeningeal metastases, unless protocol-specific conditions are met.
• Active second invasive malignancy within two years prior to screening.
• Significant cardiovascular/cerebrovascular disease within 6 months prior to study treatment start.
• Any other diseases, metabolic dysfunction, physical examination finding or clinical laboratory finding that gives reasonable suspicion of a disease or condition that would contraindicate the use of an investigational drug.
• Prior allogeneic bone marrow transplantation or prior solid organ transplantation.
• Active or history of autoimmune disease.
• Known hypersensitivity to any of the components of RO7300490 formulation or to components of atezolizumab formulation.
• Pregnancy, lactation or breastfeeding.
• Dementia or altered mental status that would prohibit informed consent.
• Major surgery or significant traumatic injury within 28 days prior to the first study drug administration (excluding biopsies) or anticipation of the need for major surgery during study treatment.
• Treatment with radiotherapy, chemotherapy, hormonal therapy, targeted therapy, immunotherapy or investigational drug concurrent or within 28 days or 5 half-lives of the drug (whichever is shorter) before the first study drug administration.