The Value of Postoperative Radiotherapy in Thymoma with Myasthenia Gravis

Abstract

For patients with thymoma combined with myasthenia gravis (MG), surgery is the first-line treatment. However, there is still debate on the effects of radiotherapy among these patients. This study is aimed to investigate the efficacy and prognosis of postoperative radiotherapy (PORT) on thymoma patients with MG. This retrospective cohort study included 126 patients with MG and thymoma from 2011 to 2021. Demographic data and information that were collected included sex, age, histologic subtype, Masaoka-Koga staging, the primary tumor, lymph node, and metastasis (TNM) staging and therapy modalities. Changes in the Quantitative Myasthenia Gravis Score (QMGs) within 3 months after treatment were used to evaluate the short-term MG symptom improvement after PORT. Minimal manifestation status (MMS) was the main endpoint of assessing the long-term MG symptom improvement. Overall survival (OS) and disease-free survival (DFS) were the primary endpoints for PORT in prognosis. Effects of PORT on MG symptom: there was a significant difference in QMG scores between non-PORT and PORT groups (χ2 = 6.300, p = 0.012). The median time to achieve MMS of patients in the PORT group was significantly shorter when compared with the non-PORT group (2.0 years versus 4.4 years [p = 0.031]). Multivariate analysis demonstrated that radiotherapy was associated with a shorter time to achieve MMS (HR 1.971, 95% CI:1.102-3.525, p = 0.022). Effects of PORT on DFS and OS: the 10-year OS rate of the whole cohort was 90.5%. The OS rates of the PORT group and the non-PORT group were 94.4% and 85.1% respectively. The 5-year DFS rates in the whole cohort, PORT group, and non-PORT group were 89.7%, 95.8%%, and 81.5%, respectively. PORT was associated with improved DFS (HR 0.139, 95% CI: 0.037-0.533, p = 0.004). In the high-risk histologic subgroup (type B2, B3), PORT exhibited better survival than non-PORT in OS (p = 0.015) and DFS (p = 0.0053). PORT remained associated with improved DFS (HR 0.232, 95% CI: 0.069-0.782, p = 0.018) in Masaoka-Koga staging II, III, and IV disease. The efficacy of PORT in patients with thymoma and MG is positive. Patients in the higher histologic subtype and Masaoka-Koga staging may benefit more obviously.