Type B2 thymomas are treated by complete resection. The biologic behavior of Type B2 thymoma is intermediate between B1 and B3 thymomas. It is often invasive at the time of diagnosis and has higher rate of recurrences and metastases than type A (spindle cell type), type AB (mixed type), and type B1 (lymphocyte-rich) thymomas. The 10-yr and 20-yr survival rates are 70-90% and 60-80% respectively. The recurrence rates for Stage I-II tumors and Stage III tumors at 10-yrs are 13% and 41% respectively. This high magnification view of a type B2 thymoma shows clusters of polygonal neoplastic epithelial cells with vesicular nuclei and punctate nucleoli. They are scattered in a lymphocyte-rich background of mostly immature T-cells.