Bemarituzumab or Placebo Plus Chemotherapy in Gastric Cancers With Fibroblast Growth Factor Receptor 2b (FGFR2b) Overexpression

Inclusion Criteria

• Adults with histologically documented unresectable, locally advanced or metastatic gastric or gastroesophageal junction cancer not amenable to curative therapy
• Fibroblast growth factor receptor 2b (FGFR2b) ≥10% 2+/3+ tumor cell staining as determined by centrally performed immunohistochemistry (IHC) testing, based on tumor sample either archival (obtained within 6 months/180 days prior to signing pre-screening informed consent) or a fresh biopsy
• Eastern Cooperative Oncology Group (ECOG) less than or equal to 1
• Measurable disease or non-measurable, but evaluable disease, according to Response Evaluation Criteria in Solid Tumors (RECIST) V 1.1
• Participant has no contraindications to mFOLFOX6 chemotherapy
• Adequate organ and bone marrow function:
• absolute neutrophil count greater than or equal to 1.5 times 10^9/L
• platelet count greater than or equal to 100 times 10^9/L
• hemoglobin ≥ 9 g/dL without red blood cell (RBC) transfusion within 7 days prior to the first dose of study treatment
• aspartate aminotransferase (AST) and alanine aminotransferase (ALT) less than 3 times the upper limit of normal (ULN) (or less than 5 times ULN if liver involvement). Total bilirubin less than 1.5 times ULN (or less than 2 times ULN if liver involvement); with the exception of participants with Gilbert's disease)
• calculated or measured creatinine clearance (CrCl) of ≥ 30 mL/minute calculated using the formula of Cockcroft and Gault ([140 - Age]) × Mass [kg]/[72 × Creatinine mg/dL]) (x 0.85 if female)
• international normalized ratio (INR) or prothrombin time (PT) less than 1.5 times ULN except for participants receiving anticoagulation, who must be on a stable dose of anticoagulant therapy for 6 weeks prior to enrollment

Exclusion Criteria

• Prior treatment for metastatic or unresectable disease (Note: prior adjuvant, neo-adjuvant, and peri-operative therapy is allowed if completed more than 6 months prior to first dose of study treatment)
• Prior treatment with any selective inhibitor of fibroblast growth factor - fibroblast growth factor receptor (FGF-FGFR) pathway
• Known human epidermal growth factor receptor 2 (HER2) positive
• Untreated or symptomatic central nervous system (CNS) disease or brain metastases
• Peripheral sensory neuropathy greater than or equal to Grade 2
• Clinically significant cardiac disease
• Other malignancy within the last 2 years (exceptions for definitively treated disease)
• Chronic or systemic ophthalmological disorders
• Major surgery or other investigational study within 28 days prior to first dose of study treatment
• Palliative radiotherapy within 14 days prior to the first dose of study treatment
• Evidence of or recent history (within 6 months) of corneal defects, corneal ulcerations, keratitis, or keratoconus, history of corneal transplant, or other known abnormalities of the cornea that may pose an increased risk of developing a corneal ulcer.