Cutaneous metastases at the sites of pembrolizumab-induced bullous pemphigoid lesions in a patient with melanoma.

The authors report a case of bullous pemphigoid (BP) that occurred during pembrolizumab therapy in a 67-year-old male patient with advanced melanoma. Following regression of BP blisters, they reintroduced anti-PD-1 treatment. Due to the flare-up of BP, immunotherapy was discontinued again and corticosteroid was restarted. As the BP lesions regressed, interestingly, new skin metastases developed, exactly where the blisters were. One year after discontinuation of anti-PD-1 treatment, considering the significant tumor progression, pembrolizumab was restarted. This induced tumor remission, while the added low-dose corticosteroid was able to prevent the recurrence of BP. The patient carries the BP-predisposing HLA-DQB1*03:01 allele. In conclusion, anti-PD-1 rechallenge may be considered in metastatic melanoma, even if restarting anti-PD-1 has previously caused the flare-up of BP symptoms.