Purpose

This is Phase 1 dose finding trial with potential dose expansion to evaluate the safety, toxicity, recommended phase 2 dose (RP2D), and maximum tolerated dose (MTD) of Neratinib plus TDxD using a standard 3+3 dose escalation design in Patients with metastatic or unresectable gastric adenocarcinoma (including GEJ tumors) that are HER2-overexpressing (IHC 3+ or IHC2+/ISH+). Patients must have progressed or been intolerant of at least one prior line of chemotherapy + HER2 directed therapy.