AB057. The practice, intent, and outcome of radiotherapy in thymic epithelial tumors—results from a national cohort

Background: Thymic epithelial tumors (TETs) are rare conditions with a wide range of clinical trajectory. Management is typically multimodal, including surgery, radiotherapy, and chemotherapy. This study aims to evaluate the utilization, indications, and outcomes of radiotherapy across various clinical scenarios in a national Danish cohort.

Methods: This descriptive study retrospectively included all patients diagnosed with TET who received radiotherapy during an 11-year period (1/1/2013–31/12/2023). We excluded patients who had radiotherapy for bone metastases or for other cancers or had follow-up of less than 2 months. The focus of this study was local control defined by the absence of progression in the irradiated area, assessed by computed tomography (CT). Radiotherapy was categorized as adjuvant (postoperative), definitive (curative intent for primary tumor or relapse), or palliative. Toxicity was reported using Common Terminology Criteria for Adverse Events (CTCAE).

Results: Seventy-nine patients with thymic tumors were included in this study. Tumor histology included thymomas, thymic carcinomas, and mixed tumors. There was a total of 98 courses. Three patients received proton therapy. Local control was achieved after 84 (86%) of all radiotherapy-courses. Of the 84 courses, 38 (39%) were followed for at least 1 year, and 26 (27%) for at least 5 years. Among the patients who achieved local control, 45 (54%) were treated in an adjuvant, 15 (18%) in a definitive, and 24 (29%) in a palliative setting. Among the 50 courses with visible tumors, complete response was achieved in 3 (6%), partial response in 16 (32%), and stable disease in 21 (42%) courses. In 45 of 48 adjuvant courses, no recurrence was observed. In the adjuvant group 27 (56%) had thymomas and 21 (44%) thymic carcinomas, consistent with the overall histological distribution. Local recurrence was observed after 12 (12%) of all courses, with 1 relapse after 5 years. Adverse effects were mostly none or mild (grade 0–1) with 4 grade 2 events and 1 grade 3 event.

Conclusions: Radiotherapy plays a crucial role in the management of TET. Radiotherapy resulted in local control in the adjuvant setting, served as a viable alternative for inoperable patients as well as provided effective palliation of symptoms in advanced cases.

Keywords: Radiotherapy; thymic epithelial tumors (TETs); local control