Value of thyroid specific peroxidase and Ki-67 stains in preoperative cytology for thyroid follicular tumors

Background The aim of this study was to elucidate immunocytochemically whether thyroid specific peroxidase (TPO) and Ki‐67 can complement fine‐needle aspiration (FNA) cytology as useful markers in order to distinguish between follicular adenoma (FA) and follicular carcinoma (FC). Methods We studied 40 FAs and 68 FCs obtained by surgical resection. FNA cytology smears were divided into two groups: Cytology‐A (Cy‐A) (94 cases) with typical benign cytology and Cytology‐B (Cy‐B) (14 cases) with atypical cytology. FCs were divided into two groups: FC‐I (42 cases) without any poorly differentiated structures and FC‐II (26 cases) with some poorly differentiated structures. Cytology smears and histology from FAs and FCs were studied immunocytochemically for thyroid specific peroxidase (TPO) and Ki‐67. Results TPO expression was negative in 12.5% FAs, 21.4% FC‐I, and 46.2% FC‐II. In 68 FC cases, Cy‐B were more frequently observed in TPO‐negative cases (38.1%) than in TPO‐positive cases (12.8%). The mean Ki‐67 LI was 0.46 in FAs, 0.53 in FC‐I, and 1.13 in FC‐II. The high Ki‐67 LI was correlated with Cy‐B. Moreover, higher Ki‐67 LI showed a close relationship with distant metastasis. In 94 Cy‐A cases, 54 cases were FCs. When 38 cases with negative TPO or Ki‐67 LI over 0.62 were extracted from them, as many as 28 cases were FCs, the rate of FCs were significantly higher than the rest. Conclusion Therefore, addition of TPO stain and Ki‐67 stain to routine Papanicolaou stain could improve the diagnostic reliability of FNA cytology for FC with high degree of malignancy. Diagn. Cytopathol. 2015;43:202–209. © 2014 Wiley Periodicals, Inc.