Fine needle aspiration biopsy for the diagnosis of thymoma metastatic to the breast: a case report.

Background: Extrathoracic metastases of thymomas are extremely rare, with only 9 documented cases in the cytologic literature, and a thymoma metastasis to the breast has not been reported before. Here we report the cytologic findings on fine needle aspiration biopsy (FNAB) for the diagnosis of a case of thymoma metastatic to the breast.

Case: A 73-year-old woman presented with a palpable mass in the right breast. A sonogram revealed a discrete, hypoechoic nodule in the upper inner quadrant of the breast. She had a history of mediastinal thymoma 2 years earlier, which was treated with chemotherapy because of inoperability. FNAB was performed: the cytologic specimen showed epithelial cell clusters with a few entrapped lymphocytes, suggestive of metastatic thymoma. However, the differential diagnosis also included a primary malignancy such as poorly differentiated ductal carcinoma or medullary carcinoma of the breast. Excisional biopsy with additional immunohistochemical staining confirmed the thymoma metastasis.

Conclusion: An FNAB-based diagnosis of this rare entity can be an appropriate, simple and minimally invasive procedure in the right clinical setting and with the appropriate patient history.