Clinical Investigation
Postoperative Radiotherapy After Surgical Resection of Thymoma: Differing Roles in Localized and Regional Disease

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Purpose

To analyze the Surveillance, Epidemiology and End Results (SEER) registry data to determine the impact of postoperative radiotherapy (PORT) for thymoma and thymic carcinoma (T/TC).

Methods and Materials

Patients with surgically resected localized (LOC) or regional (REG) malignant T/TC with or without PORT were analyzed for overall survival (OS) and cause-specific survival (CSS) by querying the SEER database from 1973–2005. Patients dying within the first 3 months after surgery were excluded. Kaplan-Meier and multivariate analyses with Cox proportional hazards were performed.

Results

A total of 901 T/TC patients were identified (275 with LOC disease and 626 with REG disease). For all patients with LOC disease, PORT had no benefit and may adversely impact the 5-year CSS rate (91% vs. 98%, p = 0.03). For patients with REG disease, the 5-year OS rate was significantly improved by adding PORT (76% vs. 66% for surgery alone, p = 0.01), but the 5-year CSS rate was no better (91% vs. 86%, p = 0.12). No benefit was noted for PORT in REG disease after extirpative surgery (defined as radical or total thymectomy). On multivariate OS and CSS analysis, stage and age were independently correlated with survival. For multivariate CSS analysis, the outcome of PORT is significantly better for REG disease than for LOC disease (hazard ratio, 0.167; p = 0.001).

Conclusions

Our results from SEER show that PORT for T/TC had no advantage in patients with LOC disease (Masaoka Stage I), but a possible OS benefit of PORT in patients with REG disease (Masaoka Stage II–III) was found, especially after non-extirpative surgery. The role of PORT in T/TC needs further evaluation.

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.

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