A case of pembrolizumab-induced bullous pemphigoid treated with dupilumab.

Immune checkpoint inhibitors are a class of drugs used in cancer treatment that promote the immune system's response by blocking the inhibitor signals from tumour cells, such as programmed cell death protein 1/programmed death ligand 1 and cytotoxic T-lymphocyte associated protein 4. Despite their clinical benefit, these monoclonal antibodies unspecifically activate the immune system and can lead to the development of 'immune-related adverse events'. Cutaneous toxicities are the most frequent immune-related adverse events, reported in approximately 30-50% of patients treated with immunotherapy; the most common dermatological toxicities are represented by rash, vitiligo, pruritus and lichenoid reactions. Usually, these reactions are mild and it is not necessary to suspend immunotherapy. Potentially life-threatening skin toxicities, such as immunobullous eruption, are rare and may appear in approximately 1% of patients. In this report we describe a case of bullous pemphigoid, the most frequent bullous disease, that developed after treatment with pembrolizumab for a metastatic melanoma. The diagnosis, first suspected by the referring clinic, was confirmed by performing serology and biopsy with direct immunofluorescence. The patient was first treated with high doses of systemic corticosteroids, without suspending the immunotherapy treatment. Subsequently, due to the continuous relapses, we decided to suspend pembrolizumab and systemic corticosteroid and to begin off-label treatment with dupilumab. The following case gives cause for reflection about the management of a drug-induced disease in an immunocompromised patient, while exploring the therapeutic options.