[Diagnosis and therapy of thymoma]

In the postoperative diagnosis of thymoma, the most important problem over the last 30 years has been whether the condition is benign or malignant. In this paper, we discussed the diagnosis of thymoma malignancy and its therapy based on our own experiences. All thymomas have the potential to be malignant. Some thymomas have low malignancy and others high malignancy. As the malignancy is therefore not uniform, it is impossible to divide thymomas into either benign or malignant categories. Masaoka, one of the present authors, introduced the concept of clinical stage to thymoma. We think that the difference between invasive and noninvasive thymomas is due to differences in the clinical stage. We also proposed a new classification of thymomas based on the degree of epithelial differentiation. This new classification reflects the malignancy of the thymoma. Both the clinical stage classification and the classification based on epithelial differentiation showed good correlations with the prognosis of thymoma can be surmised by an exact diagnosis based on these two new classifications. The most important point concerning the therapy of thymoma is radical resection of the tumor. However, reduction surgery can be the method of second choice, especially in myasthenic thymoma, because of its slow growth. We carried out irradiation in all patients with thymoma postoperatively, resulting in a low rate of recurrence of the thymoma. This indicates the effectiveness of radiation therapy for this condition.