Retrospective studies have shown immune-related adverse events (irAEs) to be associated with better prognosis. However, no prospective clinical trials have been conducted, and little is known regarding the association between irAEs and the outcome of patients with NSCLC after treatment with immunotherapy.We conducted a prospective cohort study of patients with advanced NSCLC who were treated with nivolumab between January and December 2016. The association between clinical outcome and irAEs 2 to 6 weeks after commencement of nivolumab treatment was investigated. IrAEs were assessed by at least three independent medical professionals.A total of 43 patients were enrolled, including 19 patients with irAEs 2 weeks after commencement of nivolumab treatment. Common irAEs included rash, pyrexia, and diarrhea. Programmed cell death ligand 1-positive tumor cell expression was not significantly different between patients with and without irAEs. The objective response and disease control rates were higher in patients with irAEs than in those without irAEs (37% versus 17% and 74% versus 29% [p = 0.17 and p < 0.01], respectively]). Patients with irAEs were associated with a significantly longer median progression-free survival than those without (6.4 months [95% confidence interval: 2.5-not reached] versus 1.5 months [95% confidence interval: 1.2-2.3] [p = 0.01]). These findings were comparable to those for patients with and without irAEs 6 weeks after commencement of nivolumab treatment.Early irAEs are associated with a better outcome after treatment with immunotherapy. We predicted responses to nivolumab by using early irAEs. Further research is needed to elucidate the mechanisms of these associations.
