Abstract: Background and purpose: Liquid-based cell test (LCT) is a routine method in pleural exfoliation examination, while cell block is required to perform immunohistochemistry for differential diagnosis. In this study, we used liquid-based cytology directly for immunohistochemical staining and discussed the feasibility of the method and its clinical significance. Methods: A total of 96 cases of pleural effusion were collected from 2016 to 2017 in Department of Pathology, Huadong Hospital Affiliated to Fudan University to prepare a H-E cytologic staining and white slices by PREPSTAIN thin liquid-based cell test machine. Immunohistochemical staining of cytologic white slices for thyroid transcription factor 1 (TTF1), P63, WT1, estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2), CK7, CK20, CDX2, CA19-9, P53, PAX2 and TG was performed after antigen repairing, and staining results were interpreted and analyzed with clinical history comprehensively. Results: Carcinoma was found in 46 cases, including 19 cases of lung adenocarcinoma confirmed by positive TTF1 staining (accounted for 59.3% of all carcinomas), 3 cases of squamous cell carcinoma by positive P63, 3 cases of metastatic breast carcinoma by positive ER/PR/HER2, 2 cases of metastatic ovary serous carcinoma by positive WT1/P53/ER/PAX2, 2 cases of metastatic colon adenocarcinoma by positive CDX2, 1 case of metastatic thyroid follicular carcinoma by positive TTF1/TG and 2 cases of metastatic pancreatic carcinoma by positive CA19-9. Forty-three cases of reactive mesothelial cells were confirmed by TTF1(-)/P63(-)/WT1(+) staining. There were still 7 cases hard to differentiate reactive from malignant cells after immunohistochemical staining, and 14 cases of poorly differentiated carcinoma in which the organ source cannot be determined due to no specific antigen expression, limited atypical cells and detachment in immunohistochemical procedure. Conclusion: Liquid-based cytology procedure is simpler and more time-saving than the method of cell block. The immunohistochemical result of cytology is reliable after proper antigen repairing and interpretable for the nuclear and membrane expression. Immunohistochemical staining performed using liquid-based cytology of pleural exfoliation may improve the accuracy and specificity of diagnosis and provide reliable basis for clinical treatment.

Key words: Liquid-based cytology, Immunohistochemistry, Pleural exfoliation