International Journal of Radiation Oncology*Biology*Physics
Clinical InvestigationPostoperative Radiotherapy After Surgical Resection of Thymoma: Differing Roles in Localized and Regional Disease
Introduction
Thymomas are relatively rare tumors of the upper mediastinum, arising from constituent tissues of the thymus. Thymic carcinoma is the most clinicopathologically aggressive entity arising from the thymus (1). The classification of thymoma and thymic carcinoma histology has evolved (2) and, most recently, was revised in 1999 by the World Health Organization Consensus Committee. World Health Organization histology has been shown to be an independent prognostic factor for thymomas 3, 4, 5, 6, 7, 8. Additional prognostic factors for thymomas/thymic carcinomas that have repeatedly been shown in the literature include Masaoka stage 4, 5, 6, 7, 8, 9, 10, 11 and extent of resection 5, 8, 10, 11, 12.
Therapy of thymoma and thymic carcinoma optimally involves surgical resection. Adjuvant radiotherapy (RT) has been the subject of a small randomized trial evaluating postoperative radiotherapy (PORT) showing no additional benefit to RT for Stage I disease (13). Most treatment recommendations must be based on retrospective data. Several series have shown a local control advantage of PORT for thymoma 12, 14, 15, 16, 17, 18, 19. Other authors have found no conclusive advantage of adjuvant RT for Stage II and III patients 20, 21, 22, 23, 24. Kondo and Monden (25) found no additional value of RT for completely resected thymomas and thymic carcinomas. Further investigation into the value of PORT for thymoma and thymic carcinoma is warranted.
In this study we analyzed the Surveillance, Epidemiology and End Results (SEER) registry data to determine the role of PORT for thymomas and thymic carcinomas.
Section snippets
SEER database
The SEER database is a national cancer registry overseen by the National Cancer Institute. SEER houses patient, disease, and outcome data for about 26% of the U.S. population. Seventeen geographically defined registries compose the SEER database and store information on demographics, primary tumor site, disease extent, histology, treatment course, and patient survival. The data are available for public use (26) because registries are deidentified and submitted to the National Cancer Institute
Results
SEER query of malignant thymoma/thymic carcinoma with LOC/REG SEER Stage A, microscopically confirmed, and surgery performed resulted in 1,129 patients. Limiting the query to “one primary only or first of multiple primaries” yielded 997 patients. Eliminating those patients who had a survival of 0 to 3 months resulted in 944 patients. The final number of patients for primary analysis was 901 after 43 patients were excluded for having a “radiation sequence with surgery” recorded as “prior to
Discussion
Although the SEER data have some drawbacks (as will be discussed later), they may provide valuable population-based data on incidence (34) and behavior (35) of rare malignancies, as well as surgical patterns of care (36). Data discussed herein are an example of how the SEER data may be mined for insight into how the natural history of malignancies may be altered by adjuvant therapy 37, 38. There are few large trials reported on thymoma and thymic carcinoma, so most treatment recommendations at
Conclusions
Definitive statements about the role of PORT for thymoma/thymic carcinoma cannot be made from our SEER analysis. However, our analysis, as the largest single retrospective study, does suggest no advantage of PORT for LOC thymoma/thymic carcinoma in patients with LOC (Masaoka Stage I) disease. The addition of PORT may be advantageous in patients presenting with REG disease (Masaoka Stage II–III), particularly if surgery was not radical.
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Reprints are not available from the authors.
The abstract of this study has been submitted for inclusion at the 2009 American Radium Society Annual Meeting.
Conflict of interest: none.