Pembrolizumab-induced erosive lichenoid reaction in a patient with metastatic lung adenocarcinoma: A case report

Immune-related adverse events induced by immune checkpoint inhibitors are quite common. Cutaneous lichenoid immune-related adverse events are among the most frequent. However, oral lichenoid adverse reactions are extremely rare. We herein describe a patient who was treated with pembrolizumab for metastatic lung cancer and developed an erosive oral lichenoid reaction induced by immunotherapy. An 87-year-old man treated with pembrolizumab for metastatic lung adenocarcinoma (stage IVa based on AJCC 2018) developed multifocal erosions of the oral mucosa mainly located on the buccal mucosa, palate, and inner portion of the lips with multiple small, irregular, hyperkeratotic areas. Histopathological examination showed epithelial necrosis and a dense band-like layer of an inflammatory infiltrate of lymphocytes and histiocytes within the upper dermis. Direct immunofluorescence was negative for both IgG and C3. A diagnosis of erosive oral lichenoid reaction of the mucosa induced by immunotherapy was established. Given the severity of the condition, pembrolizumab treatment was withheld and concomitant topical and systemic steroids were started. After 1 month, the drug-related toxicity was ameliorated and immunotherapy was re-introduced. Only one other case of pembrolizumab-induced erosive lichen planus of the oral mucosa has been described to date. Previously reported drug-induced lichenoid rashes were mainly localized on the skin. Clinically, the main differential diagnoses of lichenoid erosive lesions are bullous immune-related disorders and should be excluded. In our patient, histological examination combined with negative results of both direct immunofluorescence and enzyme-linked immunosorbent assays confirmed the diagnosis of erosive lichenoid drug reaction. Clinicians should be aware of lichenoid involvement of the oral mucosa because related pain and food intake difficulties may seriously compromise treatment compliance. Prompt treatment of oral drug-related reactions may prevent interruption of immunotherapy and improve patients’ quality of life.