RecruitingPhase 2Drug trialDeveloping ctDNA Guided Adjuvant Therapy for Gastrooesophageal CancerMulticentre, single arm, open label UK phase II trial to assess the efficacy of trastuzumab deruxtecan in reducing micrometastatic disease burden in HER2 positive GOA patients who are ctDNA positive after chemotherapy and surgery. 25 patients will be recruited from approximately 15 NHS secondary care sites.