Delayed immune-related adverse events in long-responders of immunotherapy: a single-center experience.

Background: Immune-checkpoint inhibitors (ICIs) often cause immune-related adverse events (irAEs). The spectrum of irAEs and their managements has been partially clarified, however the knowledge on time-course of irAEs is not well understood.
Methods: A retrospective study based on the medical record was performed. The study subjects were consisting of patients with various types of solid tumors for whom ICIs (nivolumab, pembrolizumab, durvalumab, atezolizumab, nivolumab plus ipilimumab) were used between April 2016 and October 2021. We focused on irAEs developed more than 1-year after commencement ICIs (delayed irAE group) and compared with irAEs developed within 1-year (non-delayed irAE group) in terms of types and severity of irAEs.
Results: A total of 336 patients were enrolled in the study. Eighty-eight patients (26.2%) developed irAEs and 248 did not. Most of the patients developing irAEs were treated using PD-L1/PD-1 inhibitors. Eighty-one patients (24.1%) in non-delayed irAE group and 7 patients (2.1%) in delayed irAE group developed irAEs. The median onset of irAEs in the delayed irAE group was 18.6 months (range: 13.5-24.3). The types of irAEs observed in delayed irAE group were dermatitis (2 cases), pneumonitis (2 cases), nephritis (1 case), arthritis (1 case), and gastritis (1 case). The severity of irAEs was almost mild (≤G2), but one patient (.3%) developed G3 nephritis.
Conclusion: PD-L1/PD-1 inhibitors frequently caused various irAEs but their severities were mostly tolerable. Few patients developed delayed irAE with mild toxities.
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