Type AB Thymoma
In this type AB thymoma, the spindle cell areas (type A component) and the lymphocyte-rich areas (type B component) are not sharply demarcated from one another. This patient was an adult male who presented with dyspnea and chest pain of 5-month duration. Imaging studies showed a large mass in the anterior mediastinum. There was no lymphadenopathy. Blood counts were normal. The resection specimen showed an encapsulated lobulated tumor. Flow cytometry showed a minority population of mature B-cells (about 15% of all lymphoid cells) and majority population of immature and mature T-cells (85% of the lymphoid cells). The immature T-cells constituted the bulk of T-cells and expressed both CD4 and CD8 along with TdT and CD10.