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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 oligo­residual 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.

Due to the widespread use of immune checkpoint inhibitors and the growing research efforts in this area, immune-mediated toxicity is well recognized. Nonetheless, few severe cases of oral or upper gastrointestinal tract mucosal involvement have been documented. Early recognition and prompt treatment are key to the adequate management of these patients. We present a male 93-year-old patient with an advanced head and neck tumor treated with nivolumab who developed severe oral ulcers. After discontinuation of nivolumab, he received initial steroid treatment without any significant improvement. Histopathologic analysis of the lesions revealed a pattern similar to graft versus host disease. Extrapolating the results of colchicine mouth washing in patients with active oral ulcers and Behçet’s disease, this strategy was implemented with concomitant metronomic cyclophosphamide, achieving complete ulcer resolution. Metagenomic oral bacterial sequencing during instauration of the lesions and highest extension revealed a significant decrease in microbiomic diversity and expansion of Haemophilus parainfluenzae similar to patients with active Behçet’s disease. In conclusion, oral ulcers associated with immune checkpoint inhibitors correspond to a difficult-to-treat entity that could physiopathologically be related to both graft versus host disease and Behçet’s disease.