Follow up
Similar follow-up protocol was used at each center. The patients were seen initially 1 month after surgery, then every 3 months for the first year, every 6 months for the second year and annually thereafter. The follow-up visits consisted of a physical examination and laboratory studies. Imaging modalities including chest radiography, abdominal CT or ultrasonography were applied at least every 6 months or when clinically indicated.
The primary outcome measures in this study were overall survival (OS), cancer-specific survival (CSS), recurrence-free survival (RFS), metastasis-free survival (MFS) and disease free survival (DFS). Duration of follow-up was the time from surgery to the date of death or last clinic visit.