Immune-related Myocarditis, Guillain–Barré Syndrome, and Myasthenia Gravis Exacerbation after Pembrolizumab Therapy in a Patient with Recurrent B3 Thymoma: A Case Report

Abstract Thymic epithelial tumors, including thymoma and thymic carcinoma, are rare malignancies for which platinum-based chemotherapy is the standard first-line treatment. Second-line options include chemotherapy, targeted therapy, immune checkpoint inhibitors (ICIs), or combination regimens. While thymoma has been strongly associated with paraneoplastic autoimmune disorders, previous clinical trials have demonstrated an increased risk of severe immune-related adverse events, such as myocarditis when treating thymoma patients with ICIs. Herein, we report a case of recurrent B3 thymoma in a patient who developed myocarditis, overlapping Guillain–Barré syndrome, and myasthenia gravis exacerbation after receiving a single dose of 100 mg pembrolizumab therapy. The patient recovered after steroid pulse therapy, intravenous immunoglobulin administration, and plasma exchange.