A Study of Amivantamab in People With Esophagogastric Cancer

Patients will receive amivantamab weekly for the first cycle, and biweekly subsequently at a dose of 1050mg (\<80kg) or 1400mg (\>80kg). The first day of dosing is considered Cycle 1 Day 1. Each cycle is 28 days in duration. The initial dose will be administered over 2 days to prevent infusion reactions. For patients who weigh \<80 kg, amivantamab 350mg IV will be given on Cycle 1 Day 1, and the remaining 700mg IV will be given on Cycle 1 Day 2. Patients will continue to receive amivantamab 1050mg IV once a week during Cycle 1 then biweekly (Days 1 and 15) of each subsequent Cycle. For patients who weigh ≥ 80 kg, 350mg IV amivantamab will be given on Cycle 1 Day 1 and 1050mg IV will be given on Cycle 1 Day 2. Patients will continue to receive amivantamab 1400mg IV once a week during Cycle 1 then biweekly (Days 1 and 15) of each subsequent Cycle.