This is a phase II study for patients with thymoma or thymic carcinoma thought to be at significant risk for recurrence following surgical removal. This study involves the use of combined chemotherapy and radiation therapy prior to surgery, in hopes of increasing the chances of complete resection. The chemoradiotherapy protocol is one which has been used extensively for other diseases, and the side effects are therefore well-documented. Patients with thymomas thought to be at significant risk for recurrence (by x-ray and pathology criteria) will be allowed to participate, and will undergo combined chemotherapy with radiation to the chest followed by surgical removal of the tumor and postoperative chemotherapy. The main outcome measured will be the rate of pathological complete response (e.g. no active tumor in the resected specimen) to the preoperative treatment. Patients will receive postoperative treatment based on surgical and pathologic criteria.