...Measurable or non-measurable, but evaluable disease using RECIST v1.1 Additional Inclusion Criteria for Phase 3 Only: • Histologically documented gastric or gastroesophageal junction (GEJ) adenocarcinoma (not amenable to curative therapy) • Radiographic imaging of the chest, abdomen and pelvis (computed tomography [CT] preferred, magnetic resonance imaging [MRI] acceptable) performed within 28 days (± 3 days) of treatment (C1D1) • FGFR2b overexpression as determined by a centrally performed IHC tissue test and/or FGFR2 gene amplification as determined by a centrally performed ctDNA blood based assay • Patient must be a candidate for mFOLFOX6 chemotherapy • No prior chemotherapy for metastatic or unresectable disease (except a maximum of 1 dose of mFOLFOX6 administered while waiting for results of FGFR2 testing during the Pre-Screening period) • If prior adjuvant or neo-adjuvant therapy (chemotherapy and/or chemoradiation) has been received, more than 6 months must have elapsed between the end of adjuvant therapy and the confirmation of radiographic disease progression`Phase 1 and Phase 2:1. ...

...- Fibroblast growth factor receptor 2b (FGFR2b) overexpression as determined by a centrally performed immunohistochemistry tissue test and/or FGFR2 gene amplification as determined by a centrally performed circulating tumor deoxyribonucleic acid (ctDNA) blood based assay...

The combination of bemarituzumab with chemotherapeutic regimens commonly used for treatment of patients with gastric cancer was also evaluated in the OCUM-2M xenograft model. Twice weekly bemarituzumab (5 mg/kg, IP) combined with weekly 5-fluorouracil (5-FU) (30 mg/kg, IP) and oxaliplatin (5 mg/kg, IP) demonstrated greater inhibition of tumor growth in the OCUM-2M xenograft model of gastric cancer....Bemarituzumab inhibited FGFR2 signaling and tumor growth in mice bearing FGFR2-amplified tumors (SNU-16 and OCUM-2M human gastric cancer cells, respectively).

...the efficacy of bemarituzumab monotherapy to inhibit growth of FGFR2-amplified tumors was measured….Bemarituzumab displayed therapeutic efficacy against OCUM-2M gastric tumors at all dose levels tested compared to the negative control (albumin) group….Specifically, tumor growth inhibition and tumor regression were seen starting at the 1 mg/kg dose, with complete tumor regression observed in 1/15 mice at the 1.5 mg/kg and 2 mg/kg doses...Bemarituzumab inhibited FGFR2 signaling and tumor growth in mice bearing FGFR2-amplified tumors (SNU-16 and OCUM-2M human gastric cancer cells, respectively).