INTRODUCTION: On the basis of the findings of the phase 3 PACIFIC trial (NCT02125461), durvalumab is standard of care for patients with stage III, unresectable NSCLC and no disease progression after concurrent chemoradiotherapy (cCRT). Many patients are considered unsuitable for cCRT owing to concerns with tolerability. The phase 2 PACIFIC-6 trial (NCT03693300) evaluates the safety and tolerability of durvalumab after sequential CRT (sCRT). METHODS: Patients with stage III, unresectable NSCLC and no progression after platinum-based sCRT were enrolled to receive durvalumab (1500 mg intravenously) every 4 weeks for up to 24 months. The primary end point was the incidence of grade 3 or 4 adverse events possibly related to treatment occurring within 6 months. Secondary end points included investigator-assessed progression-free survival (PFS; Response Evaluation Criteria in Solid Tumors version 1.1) and overall survival. RESULTS: Overall, 117 patients were enrolled (59.8% with performance status >0, 65.8% aged ≥65 y, and 37.6% with stage IIIA disease). Median treatment duration was 32.0 weeks; 37.6% of patients remained on treatment at data cutoff (July 15, 2021). Grade 3 or 4 AEs occurred in 18.8% of patients. Five patients had grade 3 or 4 possibly related adverse events within 6 months (incidence: 4.3%; 95% confidence interval: 1.4-9.7), including two pneumonitis cases. Two patients (1.7%) had grade 5 AEs of any cause. Survival data maturity was limited. Median PFS was 10.9 months (95% confidence interval: 7.3-15.6), and 12-month PFS and overall survival rates were 49.6% and 84.1%, respectively. CONCLUSIONS: Durvalumab after sCRT had a comparable safety profile with that observed with durvalumab after cCRT in PACIFIC and had encouraging preliminary efficacy in a frailer population.