[A Case of Recurrent Thymoma Treated with Pembrolizumab as the Fifth-Line Chemotherapy].

The option of chemotherapy for recurrent thymoma is limited. Postoperative adjuvant therapy has yet to be established. A 71-year-old male underwent extended thymectomy for thymoma with Masaoka stage Ⅲ, and subsequently, radiation was performed as adjuvant therapy in 2012. Since recurrence was detected in 2014, multidisciplinary treatment was performed for 4 years. An increase of intrathoracic dissemination was detected in 2018. Tumor tissue samples by re-biopsy showed 70% expression of programmed death-ligand 1(PD-L1). Pembrolizumab was administered as fifth-line chemotherapy every 4 weeks at a dosage of 200 mg. After 3 courses, the lesions had remarkably decreased. This suggests that pembrolizumab for thymoma with high PD-L1 expression is efficacious.