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BackgroundThere are currently no reliable biomarkers to predict the occurrence of severe complications and treatment response in patients with toxic epidermal necrolysis (TEN). Immune checkpoint inhibitor-related TEN (irTEN) is much rarer than typical TEN, but mortality rates associated with irTEN are much higher than those for TEN. TEN and irTEN should therefore be managed in a different manner.ObjectivesTo investigate biomarkers that could be used to predict outcomes and therapeutic efficacy associated with irTEN and TEN.Materials & MethodsSeven patients with TEN and two patients with irTEN were included in the study. The seven patients with TEN were treated with varying combinations and sequences of high-dose corticosteroids, intravenous immunoglobulin, pulse corticosteroids and plasma pheresis.ResultsFour of the seven TEN patients developed severe complications, and one patient eventually died due to cytomegalovirus disease. We found that, for TEN, a high neutrophil-to-lymphocyte ratio (NLR) at baseline was associated later onset of severe complications, and a subsequent decrease in NLR after starting immunosuppressive therapy was associated with a beneficial treatment response. In contrast, the opposite was found for the two irTEN patients; a low NLR at baseline and an increase in NLR after starting treatment were associated with poor outcome and a beneficial treatment response, respectively.ConclusionThe NLR may be differentially used as a practical and cost-efficient biomarker to predict treatment response and disease outcomes in patients with TEN and irTEN.