Clinical data: a 60-year-old woman was referred for an evaluation of a suspected malignant tumor of the thyroid. The goiter had evolved over 5 weeks. 

Palpation: the highly enlarged right thyroid was hard, uneven, painless.

Functional state: euthyroidism (TSH 2.38 mIU/L, FT4 13.1 pM/L).

Ultrasonography: almost the whole right thyroid was composed of a hypoechogenic nodule with echonormal areas. The latter corresponds to necrosis. 

Cytological picture: there isn't any colloid on the smear. Several irregular clusters of cells with nuclear crowding. There were a few isolated pleomorphic tumor cells on the smear.

Combined clinical-cytological diagnosis: anaplastic cancer.

Histopathology: anaplastic cancer.

Comment: the extremely rapid evolvement (i.e. within 3-8 weeks) of a painless hard thyroid is almost diagnostic for anaplastic cancer. A similar clinical presentation may caused by MALT-lymphoma, but in the latter the thyroid enlargement evolves over 2 to 4 months.