Background: Little is known about the changes in prognostic factors after adjuvant S-1 monotherapy has become widespread as a standard of care for patients with gastric cancer (GC) in East Asia. The present study compared prognostic factors of patients with stage II/III GC treated with or without S-1 adjuvant to formulate appropriate risk stratification strategies.
Methods: We designed a large multicenter dataset and retrospectively analyzed 847 patients with GC stage II or III, who underwent curative gastrectomy between 2010 and 2014. Clinicopathological features and prognostic factors were compared between the two patient groups: surgery-alone (n = 266) and S-1 adjuvant (n = 581).
Results: There were no significant differences in pathological tumor depths, nodal status, and disease stages between groups. Recurrence-free survival was significantly longer in the S-1 adjuvant group. For the surgery-alone group, independent prognostic factors were (in order of hazard ratio): (1) invasive growth, (2) high preoperative carcinoembryonic antigen levels, (3) total gastrectomy. For the S-1 adjuvant group, macroscopic tumor size (≥50 mm) was identified as another independent prognostic factor next only to pN2/3. There was overlap between the survival curves of patients with tumor size ≥50 mm in both groups. After receiving adjuvant S-1 monotherapy, ≥50 mm patients had significantly higher prevalence of peritoneal and lymph node metastasis as initial recurrences compared with <50 mm patients.
Conclusions: Adjuvant S-1 monotherapy may alter listing of adverse prognostic factors of stage II and III patients. Macroscopic tumor size ≥50 mm may serve as an important determinant for risk stratification to identify patients who require more intensive treatment.