Hobnail Variant of Papillary Thyroid Carcinoma: Case Series with Fine-Needle Aspiration Cytology and Cell-Blocks

hobnail features (HPTC) is a rare, but very aggressive variant of PTC. The cytological features of HPTCs on fine needle aspiration smears have never been described. Design: We examined smears and cell blocks of 5 cases of HPTC to define their diagnostic cytological features. B-RAF mutation was studied in all cases by pyrosequencing. Histopathological and immunohistochemical data were further obtained from surgical specimens. Follow up information were obtained from medical record review. Results: The patients (3 females and 2 males) age ranged from 27 to 86 (mean 65) years. Tumor size ranged from 2 to 9 cm (mean 4,2 cm). All aspirates were highly cellular with a bloody background and scant colloid. The cells were arranged in papillary clusters or in micropapillary groups. The proportion of isolated cells versus clusters varied from case to case. The cell population consisted of small to medium-size cells with tear-drop cytoplasm, apically placed occasionally grooved nuclei that produced a surface bulge leading to a hobnail appearance and high N/C ratio. At higher magnification, the nuclei showed variable degrees of atypia with occasional pink intranuclear holes. Nuclear stratification and atypical mitotic figures were present. B-RAF mutation was present in 3/5 cases. All cases showed positivity for Thyroglobulin, Thyroid transcription factor-1 (TTF-1), partial loss of E-cadherin expression and over-expressioin of p53 protein on histological sections. Four patients were alive without diseases and 1 patient showed a locoregional recurrence at 8.5 months (range: 2 to 24 months) of follow-up. Conclusions: A combination of papillary/micropapillary and hobnail cyto-architectural patterns of growth, single tear-drop cells, high N/C ratio, severe crowding could be the most useful criteria for diagnosing HPTC on cytological smear