INTRODUCTION: Thyroid cytology is a widely accepted tool in the clinical triaging of nodular lesions. Cell blocks (CBs) can help in the diagnosis of atypical lesions, namely, thyroid Bethesda category of Atypia of undetermined significance/follicular lesion of undetermined significance (AUS/FLUS). METHODS: In a series of 224 AUS/FLUS thyroid samples with CB, we studied CB cellularity and feasibility of 3 immunohistochemical markers (cytokeratin 19 [CK19], HBME-1, and galectin-3) apart and in combination. RESULTS: The CBs were non-diagnostic in 34 cases. Twenty-four CBs contained <10 cells, 45 CBs 10-50 cells, and 121 CBs >50 cells. Notably, more cellularity was found in CBs performed by plasma-thrombin and in-house techniques (p < 0.001). The diagnostic accuracy to detect malignancy was 65.1% for CK19, 72.1% for HBME-1, and 70.3% for galectin-3. CONCLUSION: In conclusion, CB cellularity is essential for successful immunohistochemistry application and further diagnostic workup of AUS/FLUS cases.

Department of Biology Faculty of Medicine in Pilsen Charles University Prague Pilsen Czechia

Department of Otorhinolaryngology and Head and Neck Surgery University Hospital Motol 1st Faculty of Medicine Charles University Prague Czechia

Department of Pathology Fimlab Laboratories Tampere Finland

Faculty of Medicine and Health Technology Tampere University Tampere Finland

North Estonia Medical Centre Foundation Tallinn Estonia

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