A Case of Breast Cancer Recurrence Mimicking a Thymus Tumor With Vascular Invasion

Mediastinal tumors have many differential diagnoses, making it challenging to confirm a diagnosis through imaging alone. We report a case of mediastinal recurrence of breast cancer mimicking a thymic tumor, with invasion of the left innominate vein, occurring 13 years post surgery. Given the tumor thrombus extending into the superior vena cava (SVC), surgical resection was performed to prevent life-threatening complications and to achieve definitive diagnosis and treatment. Breast cancer is known for its slow growth and late recurrence. While axillary lymph nodes (ALNs) are the most common site of breast cancer drainage, alternative pathways such as the internal mammary lymph nodes may also play a role in disease spread. Recurrence of breast cancer in IMLN can mimic mediastinal tumors, such as thymoma or thymic cancer. Therefore, in patients with a history of breast cancer, a mediastinal tumor should raise suspicion for breast cancer recurrence, even if it involves the innominate vein or occurs after a long interval.