Thymoma AB is a mixed thymoma, which includes cellular components of the spindle cell type, medullary cell type and cortical cell type categories. Whether it is benign or malignant depends on whether the thymoma grows through the envelope during surgery, whether there is infiltration with the surrounding tissues, and whether it can be completely excised to determine whether it is benign or malignant. If thymoma type AB can be removed completely without adhesion to surrounding tissues, it is a benign thymoma. If the thymoma type AB has adhesions with the surrounding tissues and invades the surrounding blood vessels, nerves and lungs and cannot be removed completely, then it is a malignant thymoma and requires radiotherapy and chemotherapy after surgery.