Case Report: A Presentation of Early-Onset Immune-Mediated Bullous Pemphigoid in a Patient with Urothelial Cancer.

Cutaneous immune-related adverse events (cirAEs) are the most common side effects of immune checkpoint inhibitor (ICI) therapy (30-50% for all grades). The vast majority of them are low or mild and can be treated without ICI interruption. Autoimmune blistering disorders, such as immune-mediated bullous pemphigoid (IBP), are rare (<1%) but potentially serious conditions that must be early detected. The onset generally occurs within the first months of the treatment, and it appears to be more common with antiprogrammed death-1 or antiprogrammed ligand 1 (anti-PD1/PDL1) than with anticytotoxic T-lymphocyte-associated protein 4 (anti-CTLA4). We present a case of a three-day severe IBP onset after receiving the first cycle of atezolizumab. This exceptional early presentation could suggest the presence of some predisposing condition and demonstrates the need to better understand predictive toxicity-related biomarkers in candidate patients for immunotherapy.