BI32 Anti-programmed death 1 inhibitor-induced squamoproliferative eruption: a rare side effect

Abstract

Cutaneous adverse events from pembrolizumab are well described. The development of multiple eruptive keratoacanthomas (KAs) and squamous cell carcinoma (SCCs) in patients treated with anti-programmed death (PD)1 inhibitors is rare. This is counter­intuitive especially when they are used to treat metastatic cutaneous SCC. It is hypothesized that this phenomenon is driven by a local cutaneous immunosuppressed tumour microenvironment. Herein, we report a case of pembrolizumab-induced eruptive squamoproliferative lesions in photoexposed sites of actinically damaged skin in a patient with metastatic melanoma. An 82-year-old male patient with stage 3C metastatic melanoma presented with multiple hyperkeratotic nodules and plaques on an erythematous base affecting his extremities, 18 weeks after commencing immunotherapy. Linear keratotic papules were noted on the palms. He has a history of oral lichen planus, which predates his melanoma and was quiescent on examination. A skin biopsy demonstrated moderately differentiated SCC. Different treatment modalities were utilized, including excision of neoplastic lesions, cryotherapy and acitretin. Pembrolizumab was stopped. The exact pathogenesis is unknown but it is proposed that anti-PD1 inhibitors may unmask actinically damaged keratinocytes. To date, treatment options are limited to case reports and include potent topical steroids, nicotinamide and acitretin. The incidence of melanoma in the Irish population is increasing and the use of anti-PD1 inhibitors has become more common. This case highlights the potential pathogenesis, histology and treatment of this uncommon side effect.