Pembrolizumab-Induced Lichen Planus in a Patient With Non-Small-Cell Lung Carcinoma (NSCLC) That Correlates to Therapeutic Response

Immune checkpoint inhibitors are increasingly being used in the treatment of various solid organ and hematologic malignancies. Dermatologic toxicities associated with programmed cell death protein-1 (PD-1) and programmed death ligand-1 (PD-L1) therapy have been widely reported in the literature. Lichen planus is an inflammatory disease frequently seen in areas of the skin and oral mucous membrane lining. This autoimmune disorder is T-cell mediated with multiple contributing factors like emotional stress, genetic predisposition, isotopic response, or drugs. With increasing use of immunotherapy, early recognition and prompt treatment of associated adverse events are critical to ensure patient safety. Cutaneous toxicities are among the most commonly observed adverse events with this class of drugs. Here, we report a case of lichen planus in a 66-year-old male patient receiving pembrolizumab for stage IV non-small cell lung cancer (NSCLC). He was diagnosed 56 months ago with advanced lung cancer with brain metastasis. He has received 62 cycles of pembrolizumab and continues to be in complete clinical and radiographic remission. Pembrolizumab is a drug that helps immune cells in killing cancer cells by binding to the PD-1 protein. This case highlights the potential cutaneous side effects that may result in a patient with pembrolizumab and the fact that it can serve as a "clinical biomarker" and show therapeutic effectiveness of the treatment.