Successful Use of Pembrolizumab to Treat Refractory Thymic Carcinoma with High PD-L1 Expression

Thymic carcinoma is a relatively rare and aggressive thymic epithelial tumor. Herein, we report successful treatment of thymic carcinoma with pembrolizumab. A 68-year-old woman was admitted to our hospital for evaluation of chest pain. Chest computed tomography showed a mass in the anterior mediastinum and lymphadenopathy in the left cervical lymph node. Analysis of biopsy specimens detected squamous cell carcinoma in the left cervical lymph node, and immunohistochemical analysis showed 100% expression of programmed death-ligand 1 (PD-L1). Masaoka-Koga stage IVb thymic carcinoma was ultimately diagnosed. Since 3 cycles of first-line chemotherapy did not result in improvement, pembrolizumab was administered as second-line treatment every 3 weeks at a dosage of 200 mg. After 3 cycles of pembrolizumab treatment, the size of the anterior mediastinal tumor and metastatic lesions had notably decreased. Pembrolizumab may prove to be an effective therapy for thymic carcinoma with high PD-L1 expression.