Clinical study on thymoma: Assessment of prognostic factors

In order to define the clinical features of thymoma, we reviewed 51 thymoma patients in our departments from 1980 to 1995. Of 146 mediastinal tumors, 51 (35%) had thymoma, the most frequent tumor, and 21 (14%) had neurinoma. Twenty-one patients had non-invasive thymoma (Masaoka staging = stage I) and 30 had invasive thymoma (stages II-IV). In the non-invasive group, the male to female ratio was 0.8 (9/12) and the majority were of mixed histologic type (13/21 = 62%). Conversely, in the invasive group, the male to female ratio was 1.7 (19/11), and the occurrence of the epithelial type (12 = 40%) was as frequent as the mixed type (13 = 43%). Patients with non-invasive thymoma were all treated with surgery only, and those with invasive thymona were treated with multimodalities except for one. The 5-year survival rate was 100% for the non-invasive group, and 67% for the invasive group. Patients with accompanying myasthenia gravis (MG) showed a better prognosis than the non-MG patients (P < 0.05). The lymphocytic type also showed a better prognosis than the epithelial type, but this was not statistically significant. The prognosis for patients with thymoma was much better than for those with thymic cancer (n = 9). Thymoma showed a variety of clinical features depending on histologic type and association with myasthenia gravis.