Isolated thymic metastasis of breast cancer 10.5 years after surgery: a case report

As breast cancer grows slowly, recurrences more than 10 years after surgery are not uncommon. However, isolated metastasis to the thymus without extra-mediastinal lesions is extremely rare.

A 51-year-old woman underwent right mastectomy for right breast cancer 10.5 years ago. Following surgery, she received adjuvant chemotherapy, radiotherapy, and 10 years of anti-estrogen therapy, with no evidence of recurrence during that period. However, due to a slow upward trend in carcinoembryonic antigen levels, PET imaging was performed and revealed an irregular tumor measuring 20 × 27 × 75 mm in diameter. This consisted of both cystic and solid components, and was located within the thymus, just above the left brachiocephalic vein, with an abnormal 18 F-fluorodeoxyglucose uptake. The tumor was confined to the thymus, with no lesions were detected in the lungs or any other organs. Differential diagnoses included thymic hyperplasia, thymoma, thymic carcinoma, and malignant lymphoma. We performed thymectomy via median sternotomy for both diagnosis and treatment. Immunohistochemical staining confirmed isolated thymic metastasis of breast cancer. The patient is currently being treated postoperatively with aromatase inhibitor and cyclin-dependent kinase 4/6 inhibitor.

We present a surgical case of an extremely rare asynchronous, isolated thymic metastasis that occurred over 10 years after initial breast cancer surgery. This case underscores the importance of considering thymic metastasis in the differential diagnosis of anterior mediastinal tumors in patients with a remote history of breast cancer.