Key Inclusion Criteria:

          -  Patient must have known histologically or cytologically confirmed and documented
             HER2-positive solid tumor excluding patients with breast cancer

          -  Advanced/metastatic cancer with measurable disease as determined by RECIST v.1.1 who
             have progressed or are intolerant to all approved therapies known to confer clinical
             benefit.

          -  Eastern Cooperative Oncology Group (ECOG) performance status ≤2.

          -  Patient must have a site of disease amenable to biopsy, and be a candidate for tumor
             biopsy according to the treating institution's guidelines. Patient must be willing to
             undergo a new tumor biopsy prior to therapy, and during therapy on this study.

        Key Exclusion Criteria:

          -  History of severe hypersensitivity to any ingredient of study drug, trastuzumab or
             other monoclonal antibody.

          -  Patients previously treated with TLR 7/8 agonist.

          -  Impaired cardiac function or history of clinically significant cardiac disease

          -  Active, known or suspected autoimmune disease.

          -  Human Immunodeficiency virus (HIV) infection

          -  History of or current interstitial lung disease or pneumonitis Grade 2 or greater.

          -  Discontinued prior checkpoint inhibitor due to a checkpoint inhibitor related
             toxicity.

          -  Currently receiving medications known to cause Torsades de Pointe that cannot be
             discontinued 7 days prior to starting treatment

        Other protocol defined inclusion/exclusion criteria may apply.