Diagnosis of thyroid metastasis of colonic adenocarcinoma by fine needle aspiration biopsy.

A case of thyroid metastasis from colonic adenocarcinoma was diagnosed by fine needle aspiration (FNA) biopsy. The FNA specimen from the thyroid nodule contained tall columnar cells consistent with the intestinal primary. Staining of the tumor cells for thyroglobulin was negative. Histologic examination of the excised nodule, which was removed due to its rapid growth and risk of skin ulceration, confirmed the FNA diagnosis. FNA biopsy in such cases should be able to distinguish between a second primary neoplasm, which would be removed, and a metastasis, which would usually not be surgically treated.