Anaplastic Thyroid Carcinoma: Cytomorphologic Features on Fine-Needle Aspiration and Associated Diagnostic Challenges.

OBJECTIVES:Anaplastic thyroid carcinoma (ATC) is an aggressive malignancy, and early diagnosis, often aided by fine-needle aspiration (FNA), is key to improving patient prognosis. While the current literature describes some of the cytologic features (CFs) of this entity, a comprehensive examination of the CFs has not yet been performed. METHODS:We retrospectively searched our electronic database for ATC cases with available slides between January 2008 and December 2019. Cases were examined for 22 CFs and compared with a control group of differentiated thyroid carcinoma. RESULTS:A total of 18 ATC cases meeting our inclusion criteria were identified. Most cases showed moderate to high cellularity (83%) and epithelioid cytomorphology (83%). Architecture included either predominantly groups/clusters of tumor cells (56%) or single tumor cells (44%). The other CFs were as follows: nuclear enlargement (100%), nuclear crowding (89%), nuclear membrane irregularities (100%), multinucleated tumor cells (33%), and background acute inflammatory cells (50%). Of the CFs examined, statistically significant differences between ATC and the control groups were found in the following: nuclear pleomorphism, coarse/clumped chromatin, macronucleoli, apoptosis, and necrosis. CONCLUSIONS:Identification of key CFs in FNA coupled with the clinical history aids in the diagnosis of ATC and helps distinguish it from other mimickers.