Inclusion Criteria:  Age ≥ 18 years Histologically or cytologically confirmed HER2-expressing advanced solid malignancy, who have been treated with at least one regimen of prior systemic therapy, or who refuse systemic therapy, and for which there is no curative therapy available. Eastern Cooperative Oncology Group (ECOG) performance status of ≤2. Completion of prior chemotherapy systemic anticancer therapy at least 2 weeks prior to study entry. Radiation therapy must be completed at least 2 weeks prior to study entry. Radiated lesions may not serve as measurable disease unless they have been radiated ≥12 months prior to enrollment. Patients must have adequate organ and bone marrow function within 14 days of first dose of study drug administration  Exclusion Criteria:  Prior anti-cancer therapy including chemotherapy, hormonal therapy, or investigational agents within 2 weeks or within at least 4 half-lives prior to IMM2902 dosing (up to a maximum of 4 weeks). Anthracyclines within 3 months before first IMM2902 dosing or lifetime load exceeding 300 mg/m² adriamycin or equivalent. Prior treatment with CD47 or SIRPα-targeting agents. Trastuzumab, pertuzumab, lapatinib, tucatinib or T-DM1 within 3 weeks before first IMM2902 dosing. Known active infection including tuberculosis, hepatitis B, hepatitis C, or human immunodeficiency virus. Known inherited or acquired bleeding disorders. History of hemolytic anemia or Evans syndrome, sickle cell disease, thalassemia, G6PD deficiency, hereditary spherocytosis, or hypersplenism in the last 3 months. Current or prior use of immunosuppressive therapy within 14 days before the first dose of IMM2902. Receipt of live attenuated vaccination within 30 days prior to registration.