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

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.