Clinical data: A 75-year-old woman was referred for an evaluation of a progressive thyroid enlargement. The patient was operated on benign nodular goiter 50 years earlier. She told us that her thyroid became enlarged a few years after the operation but until recently caused no complaints. She noticed a sudden increase in the last two months, which caused dyspnea and dysphagia.

Palpation: a very hard, almost fixed left lobe.

Laboratory tests: subclinical hyperthyroidism (TSH 0.09 mIU/L, FT4 15.7 pM/L, FT3 4.66 pM/L).

Ultrasonography. The left lobe was extremely enlarged and composed of multiple hypoechogenic nodules. The dimensions of the left lobe were 150x180x350 mm, width, depth, length, respectively.

Cytological report: anaplastic cancer.

Histopathology: anaplastic cancer.