Background: The standard adjuvant chemotherapy regimen for completely resected pathological stage II/IIIA non-small cell lung cancer (NSCLC) is four courses of cisplatin plus vinorelbine. However, the continuity and toxicity of cisplatin-based regimens remain problematic. Conversely, carboplatin-based chemotherapy is a less toxic and more tolerable regimen for various stages of NSCLC. In particular, the efficacy and tolerability of carboplatin plus S-1 in advanced NSCLC were confirmed by previous pivotal studies such as the LETS trail. Therefore, this phase II study assessed the feasibility, safety, and usefulness of carboplatin plus S-1 followed by maintenance S-1 as an adjuvant treatment. Methods: In this single-arm, multicenter phase II study, 40 patients who previously underwent complete resection of NSCLC were enrolled from November 2013 to January 2015. The chemotherapy protocol was four cycles of carboplatin (AUC 5 on day 1) and oral S-1 (80 mg/m2 every other day from days 1 to 21) followed by oral S-1 (80 mg/m2 every other day for 48 weeks). The primary endpoint was the treatment completion rate, and the secondary endpoints were adverse events and 2-year recurrence-free survival. Results: The treatment completion rate of the planned schedule was as low as 30.0% (90% confidence interval: 40.3-63.0%). The reasons for adjuvant chemotherapy discontinuation were adverse events, refusal, tumor recurrence, and other reasons in 13, 6, 10, and 2 patients, respectively. The 2-year progression-free survival rate was 66.7% among patients who completed maintenance chemotherapy. There were no treatment-related deaths, and most adverse events were less than grade 3. Conclusions: Carboplatin plus S-1 followed by S-1 maintenance for 1 year in the adjuvant treatment of NSCLC was not tolerable, although most adverse events were not severe. However, patients who can fully complete the regimen might experience clinical benefit.
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