Junichi Ishigaki

Introduction: Thymomas and thymic carcinomas are rare diseases with limited clinical evidence. This study aimed to investigate the clinical characteristics of and treatment practices for Stages III and IV thymoma or thymic carcinoma in Japan. Methods: We analyzed cases of Stage III and IV thymoma and thymic carcinoma diagnosed between 2018 and 2022 and recorded in a nationwide dataset linking the Hospital‐based Cancer Registry and the Diagnosis Procedure Combination survey. Treatment practices, including the use of perioperative chemotherapy, radiotherapy, and newer systemic therapies as well as the chemotherapy regimens, were evaluated. Results: Overall, 556 stage III thymoma, 312 stage III thymic carcinoma, 431 stage IV thymoma, and 976 stage IV thymic carcinoma patients were identified. Postoperative radiotherapy after complete resection was more common for stage III thymic carcinoma than for thymoma (34.1% vs. 10.7%), while perioperative chemotherapy was used more frequently for stage IV thymoma than for thymic carcinoma (preoperative: 15.5% vs. 3.7%; postoperative: 8.4% vs. 4.4%). For stage IV thymoma, adriamycin–cisplatin–vincristine–cyclophosphamide was the most common regimen (41.8%), whereas carboplatin–paclitaxel was predominantly used for stage IV thymic carcinoma (99.5%). The proportion of anthracycline‐based therapy for stage IV thymoma increased from 50.0% to 77.8%, while that of postoperative radiotherapy for stage III thymoma decreased from 11.1% to 4.1%. Conclusions: Evidence‐based treatment approaches for thymoma and thymic carcinoma have been widely adopted in Japan.