I have similar questions. I'm not sure what the answer is though. Repeat testing and close follow up as well as reporting of any symptoms seem most important. My husband was NED for nearly 4 years, doing well until a routine endoscopy showed recurrence. He has squamous cell type in the distal esophagus, a site more common for adenocarcinoma. He had a negative CT scan and PET this time, so if not for the endoscopy, we may not have known until symptoms developed again. I too am wondering how they will figure that out with those repeat tests after he completes treatment, since they were both negative. I would imagine repeat endoscopy...have you seen your oncologist yet about the CT scan results @merryp? Wishing you the best