Improvement of the cytological diagnostic accuracy of follicular thyroid lesions by the use of the Ki-67 proliferative index in addition to cytokeratin-19 and HBME-1 immunomarkers: a study of 61 cases of liquid-based FNA cytology with histological controls

Objectives To evaluate HBME‐1, cytokeratin‐19 (CK‐19) and Ki‐67 immunomarkers in order to increase the diagnostic accuracy of preoperative thyroid fine needle aspiration (FNA) cytology. Methods Immunocytochemistry against HBME‐1, CK‐19 and Ki‐67 was performed on 123 thyroid FNAs processed by liquid‐based cytology (LBC). Statistical analysis was carried out on 61 cases with histological control and sufficient material for one or more of the three markers. The Bethesda System was used for cytological diagnosis. Results Taking into account all the cytological categories, with a cut‐off of 30% of positive cells, HBME‐1 (n = 47) and CK‐19 (n = 53) showed a sensitivity for malignancy of 66.7% (95% confidence interval, 53.2–80.1) and 90.5% (82.6–98.4) and a specificity of 90.6% (82.3–99) and 75% (63.3–86.7), respectively. For Ki‐67 (n = 54) with a cut‐off of 1% of positive cells, the sensitivity was 85.0% (75.5–94.5) and the specificity 70.6% (58.4–82.7). In the follicular neoplasm/suspicious for follicular neoplasm (FN/SFN) category (n = 37), which was the focus of the study, papillary thyroid carcinomas (PTCs) were less numerous (four cases, three of which were the follicular variant), the positivity of the three immunomarkers combined showed an overall accuracy of 91% (21/23). The mean percentage of Ki‐67‐positive cells was increased in malignant lesions, with the exception of follicular variant PTCs: 16% ± 15.6% in two follicular carcinomas, 4.8% ± 3.2% in 13 classical PTCs, 1% ± 1.2% in five follicular variant PTCs and 0.5% ± 1.9% in 34 non‐malignant lesions. Conclusions Immunocytochemistry using HBME‐1, CK‐19 and the Ki‐67 proliferative index increased the diagnostic accuracy of FNA in the FN/SFN category of the Bethesda System, which may help to distinguish lesions in this category with a low or high risk of malignancy. Thus, clinical management would be improved.