BI04 Bullous pemphigoid induced by cemiplimab to treat metastatic squamous cell carcinoma in a renal transplant patient

Abstract A 76-year-old man was urgently referred with a widespread blistering rash. His medical history included a renal transplant in 2018 and a pT3 desmoplastic squamous cell carcinoma (SCC) on his scalp vertex measuring 7 × 8 cm, diagnosed in 2022. This was excised with an incomplete deep margin and he received adjuvant radiotherapy. Due to local metastasis to the occipital region, bilateral supraclavicular lymphadenopathy and rapid progression of his scalp SCC, cemiplimab was commenced. He completed five cycles of cemiplimab with an excellent clinical response before the onset of his bullous eruption. His dose of tacrolimus was reduced to a minimal level and mycophenolate was stopped prior to commencing cemiplimab. At presentation, there were widespread erythematous and urticated patches associated with multiple tense bullae over his trunk, arms, legs and feet. Initially there was no mucosal involvement but subsequently he developed ulceration of the right lower gingiva. The clinical appearances were suggestive of bullous pemphigoid. Histopathology of lesional skin demonstrated a subepidermal bulla with eosinophils, direct immunofluorescence demonstrated linear IgG and C3 deposition at the basement membrane, and enzyme-linked immunosorbent assays to BP180 and BP230 were positive, confirming this diagnosis. He was treated with clobetasol 0.05% ointment, doxycycline 100 mg twice daily, nicotinamide 500 mg three times daily and prednisolone 30 mg daily (equivalent to 0.3 mg kg−1 per day). While his pemphigoid responded to the above regimen, he experienced severe flares when he reduced the dose of prednisolone below 20 mg daily despite tapering this very slowly. After careful discussion with his oncology and nephrology teams, the decision to restart mycophenolate was made. Cemiplimab has not been restarted as the timing of the onset of his pemphigoid coincided with use of this treatment, and his SCC currently appears stable on clinical examination and imaging. Cemiplimab is a recombinant IgG4 anti-PD-1 human monoclonal antibody licensed for treating metastatic or locally advanced cutaneous SCC. Autoimmune blistering disorders represent approximately 1% of cutaneous immune-related adverse events (cirAEs) secondary to immune checkpoint inhibitors, and it is thought that development of certain cirAEs may indicate a more favourable treatment outcome for the underlying malignancy. There have been a small number of case reports to date of cemiplimab-induced bullous pemphigoid. The severity of disease and treatments used were variable, and in some, cemiplimab was recommenced. Management of more severe bullous pemphigoid with oral immunosuppression requires careful consideration of the underlying malignancy and additionally, in our patient’s case, chronic renal impairment following renal transplantation.