Study to Determine Safety and Dose of NJH395 in Non-breast HER2+ Advanced Cancer

This study has two parts. There will be a single dose of NJH395 in the first part and multiple doses of NJH395 in the second part. After the first part is completed, the second part may open.

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.