Anaplastic Thyroid Carcinoma: Morphologic Findings and PAX-8 Expression in Cytology Specimens

To evaluate the morphologic findings most encountered in anaplastic thyroid carcinomas (ATCs) and evaluate for the expression of PAX-8. The cytology specimens from 21 cases of ATC were evaluated for the following several cytologic criteria: cell morphology, pleomorphism, presence or absence of multinucleated cells, colloid, neutrophilic infiltrate and well-differentiated component. Immunohistochemical studies for PAX-8 were performed on cell blocks in selected cases. The most common morphology present was epithelioid, followed by spindle, multinucleated giant cell and rhabdoid, with 75% demonstrating more than 1 cell morphology. Marked pleomorphism (81%), neutrophilic infiltrate (90%) and necrosis (63%) were frequent. No nuclear grooves, colloid or well-differentiated component was identified in any case. Immunocytochemical stains for PAX-8 were negative in 5 cases in which a cell block was available. ATC is a tumor with diverse morphologic characteristics, and more than 1 cell morphology is usually present. A neutrophilic infiltrate is a common finding and represents a clue to the correct diagnosis.