Background: Anaplastic thyroid carcinoma (ATC) is a rare, aggressive tumor which arises either de novo or in a differentiated tumor such as papillary (PTC) or follicular thyroid carcinoma (FTC). Cytologic diagnosis of anaplastic transformation in well differentiated thyroid malignancy
is rarely documented.
Case Reports: Case 1: A 57-year-old male presented with history of gradually increasing, huge swelling in front of the neck of one year duration. Fine needle aspiration cytology (FNAC) revealed high cellular yield with predominantly sarcomatous pattern along with necrotic material and
occasional tiny groups of epithelial cells exhibiting follicular pattern. A cytologic diagnosis of ATC arising in FTC was made. Histopathologic examination was not done as the patient was put on palliative treatment.
Case 2: A 50-year-old female, a known case of follicular carcinoma previously operated, presented with two swellings in the thyroid region. A routine FNAC was performed to rule out recurrent FTC. FNA smears revealed clusters of cells with moderate to markedly pleomorphic malignant epithelial cells, at places exhibiting vaguely maintained follicular architecture. A few well preserved follicles along with scattered, bizarre, naked nuclei were
also noted. A cytologic diagnosis of FTC with anaplastic transformation was considered. The patient was not operated.
Conclusions: A perfectly sampled FNA material allows a diagnosis of anaplastic transformation in a preexisting follicular thyroid carcinoma.

Keywords: FNAC, thyroid, anaplastic, transformation, follicular, Carcinoma, sarcomatous, fire flares