Cytomorphologic features of poorly differentiated thyroid carcinoma

BACKGROUND: Poorly differentiated thyroid carcinoma (PDTC) is an uncommon and aggressive malignancy. Despite the significant clinical implications of a diagnosis of PDTC, its cytomorphologic features have not been well defined. Statistical analysis was applied to a series of 40 PDTCs to identify a specific set of cytomorphologic features that characterized these tumors on fine‐needle aspiration biopsy (FNAB). METHODS: In total, 40 thyroid FNABs that were highly diagnosed histologically as PDTC (19 insular carcinomas and 21 noninsular carcinomas) comprised the study group. A control group of 40 well differentiated thyroid neoplasms were selected for comparison. All FNABs were reviewed and scored for a series of 32 cytomorphologic features. The results were evaluated using univariate and stepwise logistic regression (SLR) analyses. RESULTS: In univariate analysis, 17 cytomorphologic features were identified that characterized the 40 PDTCs: insular, solid, or trabecular cytoarchitecture ( P < .001); high cellularity ( P = .007); necrosis ( P = .025) or background debris ( P = .025); plasmacytoid appearance ( P = .0007); single cells ( P < .0001); high nuclear/cytoplasmic ratio ( P < .0001); scant cytoplasm ( P = .03); nuclear atypia ( P < .0001), including nuclear pleomorphism ( P = .0052) and anisokaryosis ( P < .0001); granular/coarse chromatin ( P = .026); naked nuclei ( P = .01); mitotic activity ( P = .0001) and apoptosis ( P < .0001); endothelial wrapping ( P = .0053); and severe crowding ( P < .0001). In logistic regression analysis, severe crowding ( P = .0008) and cytoarchitecture ( P < .0001) were identified as the most significant cytomorphologic features of PDTCs, and the combination of cytoarchitecture, severe crowding, single cells, and high nuclear/cytoplasmic ratio was the most predictive of PDTC. CONCLUSIONS: PDTCs have characteristic cytomorphologic features. By using logistic regression analysis, the features that were identified as the most predictive of PDTC were severe crowding, insular/solid/trabecular morphology, single cells, and high nuclear/cytoplasmic ratio. Cancer (Cancer Cytopathol) 2009. © 2009 American Cancer Society.