• • S-1 adjuvant chemotherapy significantly improved 3-year disease-free survival (DFS) by 10.6 percentage points (72.3% vs. 61.7%; HR 0.68; 95% CI 0.55-0.84; p < 0.001) compared to observation, representing a 32% relative reduction in risk of recurrence or death.
• • Overall survival (OS) at 3 years was also significantly higher in the S-1 group (82.4% vs. 74.6%; HR 0.72; 95% CI 0.56-0.93; p = 0.012), translating to a 28% relative reduction in mortality risk.
• • The safety profile was manageable: grade 3/4 adverse events occurred in 28.4% of patients, with neutropenia (12.3%), anorexia (8.7%), and diarrhea (5.2%) being the most frequent; no treatment-related deaths were reported.
• • High treatment adherence (78.6% completed the full 1-year course) indicates that S-1 is a feasible oral adjuvant regimen, potentially improving patient compliance compared to intravenous chemotherapy, which is critical for real-world effectiveness.