Metastatic disease from primary colon cancer in the thyroid is rare. The authors have submitted such a case. What makes this case particularly unusual is that it was in a man. 80% of such cases are in women. It has been speculated that there may be a humoral component. What is even more unique in this case is that it was found during the workup of a symptomatic parathyroid adenoma. The diagnosis was confirmed with immunochemistry using markers Cytokeratin 20 (CK20), Cytokeratin 7 (CK7), and Thyroid Transcription Factor 1 (TTF-1) .
Keywords: CK20; CK7; TTF-1; metastasis to thyroid; metastatic colon cancer; parathyroid adenoma.