Supplementary Material for: Association of Programmed Cell Death 1 Inhibitor with Circumorificial Plasmacytosis

Introduction: The development of immune checkpoint inhibitors is considered one of the most important advances in cancer treatment. Pembrolizumab is an immune checkpoint inhibitor against programmed death 1 (PD-1) receptors that has demonstrated antineoplastic activity against various malignancies, including non-small cell lung cancer, melanoma, and triple-negative breast cancer. Pembrolizumab is associated with numerous adverse reactions including mucosal and cutaneous reactions referred to as immune-related adverse events. These events can impact patient quality of life, lead to dose reduction or discontinuation of the medication. A comprehensive understanding of pembrolizumab’s toxicities is crucial for the initiation of treatment. Case Presentation: We present the case of a 27-year-old man with stage IVB thymic carcinoma with a bulky anterior mediastinal mass, bilateral jugular, bilateral peri-tracheal, and bilateral cardiophrenic lymphadenopathy, and a small pericardial effusion. He received pembrolizumab IV every 3 weeks for 53 cycles over 39 months. The patient developed bleeding oral lesions approximately 38 months after treatment with pembrolizumab. Conclusion: The patient’s pembrolizumab treatment was not interrupted and the perioral rash ultimately improved after treatment with steroids.