Randomized phase II study of daily and alternate-day administration of S-1 for adjuvant chemotherapy in completely-resected stage I non-small cell lung cancer: results of the Setouchi Lung Cancer Group Study 1301

BACKGROUND: The aim of this multicenter, randomized phase II study was to analyze the feasibility and safety of alternate-day S-1, an oral fluoropyrimidine, for adjuvant chemotherapy in patients with completely resected pathological stage I (tumor diameter > 2 cm) non-small cell lung cancer (NSCLC). METHODS: Patients were randomly assigned to receive adjuvant chemotherapy for 1 year comprising either alternate-day oral administration of S-1 (80 mg/m(2)/day) for 4 days a week (Group A) or a 2-week oral administration of S-1 (80 mg/m(2)/day) followed by 1 week of rest (Group B). The primary endpoint was feasibility, which was defined as the proportion of patients who completed the allocated intervention for 6 months with a relative dose intensity (RDI) of 70% or more. RESULTS: Ninety-three patients were enrolled of whom 90 patients received S-1 treatment. Median follow-up was 66.9 months. The treatment completion rate based on an RDI of 70% or more for 6 months was 84.4% (95%CI; 70.5–93.5%) in group A and 64.4% (95%CI; 48.8–78.1%) in group B. There were no grade 4 adverse events in either group. Moderate or severe adverse events (grade 2 or grade 3) were significantly more frequent in group B (67%) compared with group A (29%, P = 0.001). The 5-year relapse-free survival rate was 87.0 and 80.9% for group A and B, respectively (P = 0.451). The 5-year overall survival rate for all patients (n = 93) was 100 and 89.4% for group A and B, respectively (P = 0.136). CONCLUSION: Alternate-day oral administration of S-1 for 1 year as adjuvant chemotherapy was demonstrated to be feasible with low toxicity in completely resected stage I (tumor diameter > 2 cm) NSCLC. TRIAL REGISTRATION: Trial registration number: UMIN000011994. Date of registration: 10/8/2013. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12885-021-08232-6.