Acute Flare of Bullous Pemphigus With Pembrolizumab Used for Treatment of Metastatic Urothelial Cancer.

In the past decade, the resurgence of immunotherapy has changed the landscape of cancer therapy. Checkpoint inhibitors targeting cytotoxic T-lymphocyte antigen-4, programmed death-1 on lymphocytes, and programmed death ligand-1 on tumors cells are currently utilized in the management of several cancers. These agents are double-edged sword with the positive effect being robust antitumor response but on the other side they can throttle up the normal immunologic homeostasis in a negative way, leading to adverse autoimmune toxicities. These adverse toxicities are frequent if patients have active autoimmune disorders. Here, we report a rare case of quiescent bullous pemphigoid which flared after initiation of pembrolizumab, a programmed death ligand-1 inhibitor.