A Study to Evaluate Safety, Pharmacokinetics and Anti-Tumor Activity of RO7300490, as Single Agent or in Combination With Atezolizumab in Participants With Advanced Solid Tumors

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.