CLINICAL TRIAL / NCT04278144

Key Inclusion Criteria: - Patient must have an advanced solid tumor with documented HER2-protein expression or gene amplification for which approved therapies have been exhausted or are not clinically indicated. - Measurable disease as determined by RECIST v.1.1. - Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1. - Tumor tissue (archival or collected prior to the study start) available for exploratory biomarker evaluation. Key Exclusion Criteria: - History of severe hypersensitivity to any ingredient of the study drug(s), including trastuzumab or other monoclonal antibody. - Previous treatment with a TLR 7, TLR 8 or a TLR 7/8 agonist. - Impaired cardiac function or history of clinically significant cardiac disease - Human Immunodeficiency virus (HIV) infection, active hepatitis B infection, or hepatitis C infection. - Active SARS-CoV-2 infection - Untreated central nervous system (CNS), epidural tumor or metastasis, or brain metastasis. Other protocol defined inclusion/exclusion criteria may apply.