Background: This study was designed to evaluate the treatment effect of S-1 following PEM-containing treatment. Methods: This retrospective study included patients with advanced (c-stage III or IV, UICC 7th) or recurrent NSCLC who received S-1 monotherapy following the failure of previous PEM-containing chemotherapy at 6 hospitals in Japan. Primary endpoint: Overall response rate (ORR). Secondary endpoint: Disease control rate (DCR), time to treatment failure (TTF), progression-free survival

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... S), and overall survival (OS). Results: A total of 53 NSCLC patients met the criteria. Forty-six patients had adenocarcinoma (88.7%) and no patients had squamous cell carcinoma. Thirty-one patients (58.5%) received the standard S-1 regimen and 18 patients (34.0%) received the modified S-1 regimen. ORR was 1.9% (95% confidential interval (CI): 0.00-10.1%). Median TTF, PFS, and OS were 65 days, 84 days, and 385 days, respectively. Conclusion: Although there were several limitations in this study, the ORR of S-1 after PEM in patients with non-SQ NSCLC was low compared to the historical control. It might be one of the choices to avoid S-1 treatment in PEM-treated patients who need tumor shrinkage.