Outcomes and Toxicities of Definitive Radiation Therapy for Unresected Thymic Malignancies

Introduction: Thymic malignancies are primarily managed with surgery. Some patients are medically inoperable or technically unresectable. We report the characteristics and outcomes of patients with unresected thymic tumors treated with definitive radiation therapy (RT) at our institution. Methods: Patients treated with curative-intent RT for unresected thymic tumors between 1997 and 2023 were identified. Age at diagnosis, sex, histology, Masaoka or TNM stage, WHO classification, reason for no resection, RT dose and fractionation, presence of paraneoplastic syndrome, chemotherapy use, and toxicities were extracted. Overall and local failure-free survival, patterns of progression, and treatment toxicities were assessed. This retrospective chart review did not require informed consent. Results: A total of 33 consecutive patients were identified (16 females and 17 males) with a median age of 61 years at diagnosis. Overall, 22 patients had thymoma and 11 had thymic carcinoma. T stage was T2 (one), T3 (seven), and T4 (25); N stage was N0 (15), N1 (one), and N2 (17); M stage was M0 (21), M1a (eight), and M1b (four). Median tumor size was 8.1 cm. Three patients were medically inoperable; 30 were technically unresectable. Of the 33 patients, 29 received chemotherapy. The median RT dose was 60 Gy in 2 Gy fractions.Furthermore, 6% developed a grade 3 toxicity and 9% developed grade 2 pneumonitis. No grade 4/5 toxicities were observed. The 2-year overall survival was 69% (95% confidence interval [CI]: 52-92) and 5-year overall survival was 56% (95% CI: 37-85). The 3- and 5-year local failure rates were 20% (95% CI: 6.9-39). Conclusions: In the most advanced stage and one of the largest reports to date, definitive chemo-RT provides high rates of local control in patients with unresected thymic malignancies.