Programmed cell death protein-1 inhibitor–induced granuloma annulare and hypertrophic lichen planus masquerading as squamous cell carcinoma

Pembrolizumab is a humanized monoclonal antibody against programmed cell death protein-1 (PD-1) and is an effective treatment for advanced non–small cell lung cancer1 and advanced melanoma.2 PD-1 functions as a checkpoint of the effector stage of the immune system and inactivates T cells when they reach tumors.2 Systemic adverse events of checkpoint inhibitors include fatigue, fever, chills, and infusion reactions. Skin rash is the most common immune-related adverse event associated with checkpoint monoclonal antibody therapy, which can manifest as maculopapular rash, urticarial dermatitis, lichenoid dermatitis, bullous pemphigoid, Stevens-Johnson syndrome, and toxic epidermal necrolysis.2, 3 We report a case of hypertrophic lichen planus (HLP) mimicking squamous cell carcinoma (SCC) as well as granuloma annulare (GA) associated with pembrolizumab.