PURPOSE Our aim in this study was to identify independent prognostic factors for overall survival (OS) in order to explain the heterogeneity of OS in patients with metastatic thymic epithelial tumor (TET).

METHODS Sixty-one consecutive patients with histologic diagnosis of Masaoka stage IV TET between January 1980 and March 2009 were analyzed at a single institution. Masaoka stage IVa was defined as pleural or pericardial dissemination, and IVb as lymphogenous or hematogenous metastasis. Metastasis outside the thoracic cage was defined as extrathoracic metastasis. To identify prognostic factors, relationships between clinicopathologic factors and outcomes were analyzed.

RESULTS Of the 61 patients, 30 (49.2%) had thymoma, 28 (45.9%) had thymic carcinoma, and the remaining 3 (4.9%) had an unclear histologic subtype. The Masaoka stage was IVa in 27 patients (44.3%) and IVb in 34 patients (55.7%). Significant independent adverse prognostic factors for OS were histologic subtype and extrathoracic metastasis (hazard ratio [HR]=3.09 and 6.03, 95% CI: 1.41-6.74 and 1.89-19.30, p=0.005 and 0.002, respectively). The presence of extrathoracic metastasis was also an independent prognostic factor for decreased progression-free survival time (PFS) (HR=6.62, 95% CI: 1.19-24.17, p=0.004). The only significant criterion for prognostic discrimination was the presence of extrathoracic metastasis in metastatic TET.

CONCLUSIONS Significant independent prognostic factors for lower OS were the histologic subtype of thymic carcinoma and the presence of extrathoracic metastasis. A new concept of extrathoracic metastasis might provide additional information for the understanding of metastatic TET.