He needs adjuvant chemotherapy for improving survival. Consultant your oncologist.

For a pT3 disease , standard protocol include adjuvant chemotherapy . Don’t consider this as an extra therapy , rather it’s part of the treatment and patient needs that to give good disease control and prognosis. Currently from the information you provided , no indication for radiotherapy. As I expect adequate lymph node area are covered in your surgery as well all margins are negative (from the information given above ) . Chemotherapy is very essential part of therapy for gastric malignancy , so defaulting that can affect survival . So very important for the patient to continue treatment . Reports not originally seen , can give you more detailed opinion and explain all options of treatment over consult , if needed please share pre operative endoscopy as well imaging reports and consult .