Thymic metastasis of breast cancer 22 years after surgery: a case report

We report a rare case of thymic metastasis of breast cancer. A 68-year-old woman, who had undergone surgery for cancer in her right breast and had been free of recurrence for 22 years, was noted to have an abnormal shadow on a chest X-ray at a regular medical checkup. Further workup, including chest CT, revealed a 22 × 18-mm mass in the anterior mediastinum. Fluorine-18-fluorodeoxyglucose-PET showed increased fluorine-18-fluorodeoxyglucose uptake that was highly suggestive of thymoma. Thoracoscopic thymothymectomy was performed. The tumor had invaded the pericardium, which was also resected. A small nodule was found in the right lung, and it was also resected. The intraoperative frozen-section diagnosis was breast cancer metastasis to the thymus and lung. The pathological diagnosis was luminal A solid tubular carcinoma (strongly estrogen receptor and progesterone receptor positive, HER2 negative) with an MIB-1 index of less than 5%. After surgery, the patient was treated with an aromatase inhibitor. As of August 2013, she has been free of recurrence for more than 36 months. It is extremely rare for breast cancer to metastasize to the thymus more than 20 years after surgery.