Clinical data: a 75-year-old woman was referred for aspiration cytology. The patient was operated for colon cancer 3 years earlier. A metastatic focus in the liver and a cystic nodule in the thyroid was discovered on FDG-PET examination.

Palpation: an elastic nodule in the right side of the isthmus.

Functional state: euthyroidism with TSH 3.27 mIU/L.

Ultrasonography: a mixed solid cystic nodule in the right side of the isthmus.

Cytology: 0.5 ml brownish fluid was aspirated. A few cell-fragments was found in dirty background. The fragments resembled a palisading cell-structure. The nuclei within the clusters were elongated. Wash-out of the needle and the cystic fluid yielded undetectable level of thyroglobulin.

Cytological diagnosis: metastasis of colon cancer.