Refractory Bullous Pemphigoid in a Patient with Metastatic Lung Adenocarcinoma Treated with Pembrolizumab

We present the case of a 73-year-old male patient with a history of tobacco use who presented with a central nervous system mass that was confirmed to be a lung adenocarcinoma metastasis. High PD-L1 expression as well as negativity to other targetable drivers led to initiation of pembrolizumab monotherapy and ablative stereotactic radiation therapy on oligo-residual disease, achieving a complete response after 2 years of therapy. Following discontinuation of systemic treatment, the patient developed widespread desquamative plaques. A skin biopsy revealed subepidermal blistering and eosinophilic infiltration in conjunction with C3 and IgG depositions on the basement membrane, detected by immunofluorescence. A diagnosis of bullous pemphigoid was obtained, and systemic corticosteroids were administered with lesion progression. Infliximab was also administered without meaningful clinical improvement. Metronomic cyclophosphamide achieved a complete resolution of skin lesions and up to this day the patient continues with tumor control and is free of dermatological findings. In conclusion, bullous pemphigoid is a very rare dermatological adverse effect related with pembrolizumab treatment. Only two cases, including this one, have been reported, especially with this medication for the treatment of non-small cell lung cancer. With more reported cases, management strategies can be optimized even in the steroid refractory setting.