Association Between S-1 Treatment Duration and Disease Control in Advanced Non-small-cell Lung Cancer.

Background/Aim: S-1 monotherapy is used for a subset of patients with advanced non-small-cell lung cancer (NSCLC); however, predictors of prolonged treatment and survival remain unclear. The aim of this study was to investigate clinical factors associated with extended S-1 treatment and clinical outcomes in patients with advanced NSCLC. Patients and Methods: We retrospectively reviewed the data of 32 patients with stage IIIB/IV or recurrent NSCLC who received S-1 monotherapy at Kanazawa Medical University Hospital from January 2015 and December 2025. Patients were classified into a long-term treatment group (≥90 days, n=13) or a short-term treatment group (<90 days, n=19). Results: Overall, the median duration of treatment was 103.4 days (range=12-342 days), the objective response rate was 12.5%, and the disease control rate was 46.9%. Baseline characteristics were generally comparable between the two groups. The study endpoints, including disease control rate and overall survival, were significantly improved in the long-term treatment group. The disease control rate was significantly higher for the long-term group than for the short-term group (84.6% vs. 21.1%, p=0.001). The median overall survival was also significantly longer for the long-term group (1,529 vs. 733 days, p=0.003). Treatment-related adverse events were mild: no grade ≥3 toxicities or treatment-related deaths were observed. Conclusion: Prolonged S-1 treatment was associated with improved disease control and longer overall survival in patients with advanced NSCLC. These findings suggest that disease stabilization, rather than tumor shrinkage, may be a key determinant of the long-term benefit of S-1 monotherapy.