BI-1607 in Combination with Trastuzumab in Subjects with HER2-positive Advanced Solid Tumors

Main Inclusion Criteria: * Is willing and able to provide written informed consent for the trial. * Is ≥18 years of age on day of signing informed consent. * Has received standard of care or is intolerant to standard of care antineoplastic therapy. Subjects who are intolerant to trastuzumab cannot be enrolled in the study. * Has at least 1 measurable disease lesion as defined by RECIST v1.1 criteria. * Has a locally confirmed HER2+ tumor. * Must have progressive disease after the last line of treatment. In addition, subjects must have received the following previous lines of treatment: 1. Prior lines of treatment including trastuzumab and chemotherapy. 2. At least one prior line of treatment with an antibody-drug conjugate (ADC) (eg, trastuzumab-emtansine \[TDM-1, or trastuzumab-deruxtecan\]). Main Exclusion Criteria: * Needs doses of prednisolone \>10 mg daily (or equipotent doses of other corticosteroids) while on the trial other than as premedication. * Has known active central nervous system (CNS) metastases and/or carcinomatous meningitis. * Has cardiac or renal amyloid light-chain amyloidosis. * Has had clinically significant lung disease requiring systemic corticosteroid treatment within the last 6 months of enrollment. * Has an active, known, or suspected autoimmune disease. * Is at high medical risk because of nonmalignant systemic disease including severe active infections on treatment with antibiotics, antifungals, or antivirals. * Has presence of chronic graft versus host disease. * Has had an allogenic tissue/solid organ transplant. * Has uncontrolled or significant cardiovascular disease. * Has a known additional malignancy of another type, except for adequately treated cone-biopsied carcinoma in situ (eg, breast carcinoma, cervical cancer in situ), adequately controlled superficial bladder cancer, and basal or squamous cell carcinoma of the skin. * Has a diagnosis of primary or acquired immunodeficiency disorder or is taking any other form of immunosuppressive therapy.