[WHO classification in thymoma]

WHO classification of thymic epithelial tumors have been shown to reflect their oncological behaviors, and type A, AB and B1 tumors have better prognosis than type B2 and B3 tumors, suggesting the significance of this classification in the clinical practice of thymomas. Type B tumors are more invasive than type A and AB tumors. Type B1 and B2 tumors are frequently associated with myasthenia gravis while type A and AB tumors are not. The findings of computed tomography (CT) imaging revealed that type A and AB tumors tend to be round and have the smooth surface while type B1, B2 and B3 tumors are often flat and have irregular surface. Type AB, B1 and B2 tumors possess a significant number of CD4+CD8+ double positive T cells in the tumor. These observations are supposed to be useful for preoperative evaluation of WHO classification of thymomas, and to help the clinicians decide application of preoperative therapy and the method of surgical resection including endoscopic surgery.