Pembrolizumab-Induced Lichen Planus: A Rare Immune-Related Adverse Side Effect

Pembrolizumab is the first anti-programmed death protein-1 agent approved by the US Food and Drug Administration. It has demonstrated efficacy in melanoma, lung cancer, and other advanced solid tumours and hematologic malignancies. Various dermatological side effects including pruritus, maculopapular rash, vitiligo, lichenoid skin reactions, psoriasis, and rarely life-threatening conditions like bullous pemphigoid, Stevens-Johnson syndrome, and drug rash with eosinophilia and systemic symptoms have been reported. We report a case of pembrolizumab-induced lichen planus in a 54-year-old female who was receiving pembrolizumab for management of lung metastasis from squamous cell carcinoma of the buccal mucosa. The lichen planus responded to acitretin and pembrolizumab was continued safely.