Radiation Therapy Increases Survival in Surgically Treated Localized Invasive Thymomas and Thymic Carcinomas: An Analysis of the SEER Database
Joshua E. Meyer1, John R. Rutledge, Jr.2, Dattatreyudu Nori1
1Arnold Center for Radiation Oncology, New York Hospital of Queens
2Department of Public Health, Weill Cornell Medical College
Purpose: Invasive thymoma (IT) and thymic carcinoma (TC) are seen infrequently in clinical practice. Consequently, few large series have been reported regarding their adjuvant treatment with radiation therapy (RT). We undertook an analysis of the Surveillance Epidemiology and End Results (SEER) database in order to attempt to identify a cohort of patients for whom adjuvant RT would increase survival.
Methods: The SEER registry database (1988-2005) was queried for cases of surgically resected IT and TC. Only cases without lymph nodal involvement or distant metastases were analyzed. The end point of the study was overall survival. The total number of patients analyzed was 798, with a median age of 58. There were 682 IT patients and 116 with TC. Disease was confined to the thymus in 178 patients, extending into adjacent connective tissue in 180, and invading adjacent structures in 368. The remaining 72 patients were described as “localized, NOS.” RT was administered to 522 patients, and 276 patients did not receive RT.
Results: Using Kaplan-Meier analysis, we found the five-year overall survival among patients with invasion into adjacent connective tissue was increased with RT (89% vs. 81%, p=0.01). This increased five-year survival with RT was also seen in patients with tumors invading adjacent organs or structures (70% vs. 61%, p=0.03). However, RT did not improve survival when the tumor was confined to the thymus. Stratifying patients by histology did not identify a group that benefited from RT. Cox proportional hazards regression analysis revealed higher age (p<0.0001, HR=1.04) and higher tumor stage (p<0.0001, HR=2.59) as significant predictors of decreased survival on multivariate analysis. Additionally, RT remained a significant predictor of increased survival on multivariate analysis (p=0.002, HR = 0.6).
Conclusion: Analysis of SEER data demonstrated a survival benefit for the use of adjuvant RT over surgery alone in localized IT and TC invading beyond the thymic capsule. This large retrospective series lends support to the practice of adjuvant RT in stage II and III patients.