2549 - Evaluating the Efficacy of Postoperative Radiotherapy in Thymoma Patients with Myasthenia Gravis

Purpose/Objective(s): This study aims to investigate the role of postoperative radiotherapy (PORT) compared to surgery alone in improving symptoms of patients with thymoma and myasthenia gravis (MG).

Materials/Methods: In this prospective observational study, patients with surgically resected and pathologically confirmed thymomas, as well as those diagnosed with concomitant myasthenia gravis by neurologists, were included. Demographic data and other relevant information were collected. The short-term improvement of MG symptoms after PORT was evaluated using changes in the Quantitative Myasthenia Gravis Score (QMG) within three months of treatment. Achieving minimal manifestation status (MMS) within two years after treatment was the primary endpoint for assessing long-term MG symptom improvement.

Results: From January 2022 to October 2024, a total of 53 patients were included in the study. These included 5 type AB thymoma (9.4%), 5 type B1 (9.4%), 28 type B2 (52.8%), 13 type B3 (24.5%), and 2 unknown type (3.7%). Among them, 30 patients received PORT, while 23 patients underwent surgery only. There were no statistically significant differences between the PORT and non-PORT groups in terms of gender, Masaoka-Koga staging, TNM staging, surgical resection status, MG subtype, or preoperative QMG score. However, there was a statistically significant difference in the distribution of histological types between the two groups, indicating a higher risk in the PORT group. Univariate analysis showed a statistically significant difference in QMG scores after treatment between the non-PORT and PORT groups (p=0.0408). The median time to achieve MMS for the entire cohort was 14 months (95% CI 12-17). Considering long-term efficacy, univariate analysis indicated that PORT was not an independent factor for achieving MMS (p=0.132). Furthermore, in the high-risk subtypes (B2+B3 types), short-term improvement in MG symptoms was also observed after PORT (p=0.04).

Conclusion: In conclusion, PORT improves short-term symptoms in patients with thymoma and MG. However, continued follow-up is accessary to assess long-term efficacy.