Trained investigators performed the postoperative follow-ups through mailings, telephone calls, home visits or outpatient services. The majority of patients routinely underwent physical examinations, laboratory testing (including CA19-9, CA72-4, and CEA levels), chest radiography, abdominal US or CT, and an annual endoscopic examination. Overall survival (OS) was calculated from the day of surgery until death or until the final follow-up date of June 2016, whichever occurred first.