Erythema multiforme as a rare skin manifestation during pembrolizumab treatment: a case report and literature review

We report the case of a 77-year-old man with recurrent oral squamous cell carcinoma who developed erythema multiforme (EM) following his third dose of pembrolizumab (PBZ). The patient presented with a widespread skin rash characterized by erythematous papules and plaques that evolved into targetoid lesions, with no mucosal involvement or systemic symptoms. The treatment with a tapering dose of prednisolone resolved the rash without interrupting PBZ therapy. The report reviews the existing literature on PBZ-induced EM as a rare cutaneous toxicity associated with immune-checkpoint inhibitors (ICIs). Prompt recognition and appropriate management of EM are crucial. The discussion emphasizes the importance of distinguishing it from more severe conditions such as toxic epidermal necrolysis or Stevens-Johnson syndrome. Decisions regarding the continuation of PBZ therapy should be made collaboratively by dermatologists and oncologists, considering the patient’s overall health and cancer treatment plan.Key Points Immune-checkpoint inhibitors like pembrolizumab have revolutionized cancer treatment, though skin toxicities can complicate therapy. EM is a rare side effect of pembrolizumab, occurring in only 0.1% of patients, usually without affecting mucous membranes. Cases of pembrolizumab-induced EM vary in severity but generally respond well to corticosteroids. Quick identification of EM is essential, and treatment continuation should be carefully considered based on cancer type and severity.