Application of cell block preparation in effusion cytology: Analysis of mismatched diagnosis and utility of immunostaining

Objective: To analyze the mismatched cases between liquid-based cytology (LBC) and cell block in effusion cytology and to confirm the utility of cell block. Methods: One hundred eighty-two samples of effusions were examined. Cell blocks were prepared from residual samples after LBC preparation, and the details about the diagnostic concordance and difference in cytological characteristics were investigated. Cell block immunostaining was performed to predict the histological type and the primary site of the carcinoma in 32 cases. ALK rearrangement and EGFR mutation were also analyzed using the cell block. Results: The diagnostic concordance rate between LBC and cell block was 97.3%. Diagnoses using LBC and cell block were mismatched in five cases. By immunostaining, the histological type was determined in 91.0% of carcinomas, and primary sites were identified in 76.5% of adenocarcinomas. ALK rearrangement was examined in two cases of lung carcinoma and EGFR mutation was examined in four cases of lung carcinoma. Conclusion: A high concordance rate between LBC and cell block in effusion cytology was found. The main cause of the mismatched diagnosis was the small amount of atypical cells in LBC or cell block. We also showed the utility of cell block in immunostaining and DNA analysis. Key word: cell block, liquid-based cytology, pleural effusion, peritoneal effusion, immunohistochemistry.