Hypertrophic lichen planus–like eruption secondary to pembrolizumab for metastatic melanoma

A 52-year-old man presented with a new skin eruption primarily affecting the chest, upper extremities, palms, and soles. He previously received pembrolizumab for 3 months for metastatic melanoma, the last infusion of which coincided with the onset of rash. Physical examination revealed scaly, annular erythematous to violaceous plaques predominantly located on the forearms, hands, and feet, with lesser involvement on the chest. Small white papules were present on the buccal mucosa. A punch biopsy was obtained from the left arm.