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.