A Study of Runimotamab in Participants With Locally Advanced or Metastatic HER2-Expressing Cancers

Inclusion Criteria

* Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1
* Life expectancy of at least 12 weeks
* Adequate hematologic and end-organ function
* Acute, clinically significant treatment-related toxicity from prior therapy must have resolved to Grade \</=1 prior to study entry
* Left Ventricular Ejection Fraction (LVEF) \>/=50%

HER2-Expressing Breast Cancer-Specific Inclusion Criteria

* Locally tested, Human Epidermal Growth Factor Receptor 2 (HER2)-expressing BC
* Locally advanced or metastatic BC that has relapsed or is refractory to established therapies

HER2-Expressing Gastric/Gastroesophageal (GEJ) Cancer-Specific Inclusion Criteria

* Adenocarcinoma of the stomach or GEJ with inoperable locally advanced or recurrent and/or metastatic disease, not amenable to curative therapy
* HER2-expressing tumor (primary tumor or metastasis) as assessed by local lab testing
* HER2-positive gastric/GEJ cancer must have received prior trastuzumab, cisplatin (or carboplatin or oxaliplatin or investigational platinum agent) and 5-fluorouracil (5-FU)/capecitabine

HER2-Positive Solid Tumor Specific Inclusion Criteria

* HER2-positive tumor (primary tumor or metastasis) as assessed by local (non-central) laboratory testing
* Locally advanced, recurrent, or metastatic incurable malignancy that has progressed after at least one available standard therapy; or for whom standard therapy has proven to be ineffective or intolerable, or is considered inappropriate; or for whom a clinical trial of an investigational agent is a recognized standard of care; or for whom a clinical trial of an investigational agent is considered an acceptable treatment option

Exclusion Criteria

* Pregnant or breastfeeding, or intending to become pregnant during the study or within 140 days after the last dose of runimotamab
* Significant cardiopulmonary dysfunction
* Known clinically significant liver disease
* Positive for acute or chronic Hepatitis B virus (HBV) infection
* Acute or chronic Hepatitis C virus (HCV) infection
* Human Immunodeficiency Virus (HIV) seropositivity
* Poorly controlled Type 2 diabetes mellitus
* History of ventricular dysrhythmias or risk factors for ventricular dysrhythmias
* Current treatment with medications that are well known to prolong the Q-wave/T-wave (QT) interval
* Known clinically significant liver disease
* Primary central nervous system (CNS) malignancy, untreated CNS metastases, or active CNS metastases (progressing or requiring corticosteroids for symptomatic control)
* Leptomeningeal disease
* Spinal cord compression that has not definitively treated with surgery and/or radiation
* History of autoimmune disease
* Prior allogeneic stem cell or solid organ transplantation