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.

          -  Active second malignancy requiring anticancer treatment and/or palliative supportive
             care.

          -  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.