An anterior mediastinal tumor was incidentally found in a 58-year-old asymptomatic woman on a medical checkup. Computed tomography (CT) demonstrated a large tumor plugging the almost entire lumen of the superior vena cava (SVC), and 3 nodules in the bilateral lungs. The tumor seemed most likely an advanced thymoma or thymic carcinoma extending into the SVC and presenting with lung metastases. The patient underwent a combined resection of the invasive tumor and the SVC under cardiopulmonary bypass (CPB), and lung wedge resection for the nodules. The bilateral brachiocephalic veins were reconstructed with the separate grafts. The invasive tumor and the lung nodules were histologically confirmed as thymoma. Resection and reconstruction of the SVC was successfully performed under CPB for extirpation of an invasive thymoma with extensive intracaval growth. Combination chemotherapy for the relapsing lung metastases finally achieved complete response 41 months after surgery.