Thymoma staging is often divided into non-invasive thymoma and invasive thymoma; its staging often adopts the Japanese Masaoka staging method, which is divided into stages I, II, III and IV. 1. Stage I shows that the tumor is confined to the thymus and has not yet broken through the thymic epithelium. 2. Stage II shows that the tumor breaks through the thymic epithelium; among them, stage IIA just breaks through the thymic epithelium and has not yet invaded the extrapleural adipose tissue; stage IIB shows that the tumor not only breaks through the thymic epithelium, but also invades the peripheral adipose tissue of the extrapleural area. 3. Stage III shows that the tumor breaks through the fat tissue and invades the surrounding organs; Stage IIIA only invades the peripheral arteries, trachea, lungs and heart; Stage IIIB shows that the tumor invades the pleura, and the patient develops pleural effusion, but the invasion is only confined to the pleural cavity. 4. Stage IV shows distant metastases such as bones and liver. Thymoma is considered malignant, and the higher the stage, the higher the degree of malignancy. When thymoma occurs, it is necessary to consult a doctor in time, complete relevant examinations and carry out standardized treatment under doctor’s guidance.