Clinical presentation: A 71-year-old man was referred for an evaluation of a suspected thyroid carcinoma. He suffered from progressive dyspnea for 3 months and discovered a large nodule in the left lobe. Laryngology revealed palsy of the left recurrent nerve.

Palpation: a hard fixed mass in the left thyroid.

Functional state: euthyroidism with TSH-level 0.83 mIU/L.

Ultrasonography. An extremely large, hypoechogenic mass occupied or infiltrated the left thyroid lobe. The mass had irregular borders.

Cytological diagnosis: carcinoma.

Wash-out thyroglobulin resulted in undetectable level.

Final diagnosis: secondary carcinoma of the thyroid, probable a metastatic adenocarcinoma.

CT examination revealed a tumor in the left upper lobe of the lung.

The patient underwent perthoracal biopsy of the mass in the lung. The biopsy of the lung: poorly differentiated adenocarcinoma cancer.