Laryngeal Mucous Membrane Pemphigoid as an Immune-related Adverse Effect of Pembrolizumab Treatment.

Pembrolizumab is an immune checkpoint inhibitor (ICI) approved for multiple indications in a variety of malignancies. Although generally well tolerated, the potential for significant adverse effects, specifically immune related adverse effects (irAEs) needs to be taken into consideration. Several cases of bullous pemphigoid have been reported as a cutaneous adverse effect of ICIs since 2015, and there are recent reports of mucous membrane pemphigoid (MMP). We present the case of an 84-year-old male with metastatic urothelial carcinoma on treatment with pembrolizumab, who developed laryngeal mucous membrane pemphigoid as an irAE. The diagnosis was based on patient's clinical history and serologic testing, and supported by symptomatic improvement after ICI discontinuation and immunosuppression. Pembrolizumab-induced MMP is a newly described and infrequent irAE, requiring early suspicion and close monitoring for its diagnosis and management.