Fine needle aspiration biopsy of neuroendocrine breast carcinoma metastatic to the thyroid. A case report.

Background: Tumors showing neuroendocrine differentiation arise in a wide range of organs, and metastatic neuroendocrine tumors may be difficult to differentiate from primary tumors. This report describes an unusual case of metastatic breast carcinoma with neuroendocrine differentiation that presented as a solitary thyroid nodule. The diagnosis was made by fine needle aspiration biopsy (FNAB).