Stomach cancer

My father is infected by adenocercinoma (cancer) in his stomach(prepyleric area).this in moderate stage and well differentiated. I showed the report to several doctors.All of them advised me to do surgery.My father is suffering from digestive problem last four months  and constipation for long time.He has no diabetic and heart is in good condition.We did diagnosis couple of weeks back and confirmed about the cancer.Should I let my father to go for surgery first or Chemotherapy than surgery?
Hashan