Abstract:Objective To examine the cytopathology and Thyroid Transcription Factor (TTF-1), Cytokeratin 7 (CK7), Cytokeratin 5/6 (CK5/6) and P63 in the pleural effusion by the Thin-Cytologic Test (TCT) and the immunohistochemistry method, and then to evalue the clinical application of these combined method in diagnosing malignant pleural effusion caused by non-small cell lung cancer (NSCLC) classification diagnosis. Methods Firstly, we screened out 281 cases of suspected tumor cells and tumor cells by the TCT method from 703 pleural effusion cases. Secondly, we tested the TTF-1, CK7, CK5/6 and P63 by the immunohistochemistry method in the 137 cases pleural effusion caused by confirmed NSCLC to classify adenocarcinoma and squamous cell carcinoma. Finally, we calculated the area under the curve (AUC) and evalued the clinical diagnostic value. Results We found 137 malignant effusion cases caused by NSCLC from 703 pleural effusions cases, including 110 cases of lung adenocarcinoma, 25 cases of lung squamous cell carcinoma and 2 cases of lung adenosquamous carcinoma. The positive rates of CK5/6, P63, TTF-1 and CK7 in malignant pleural effusion caused by lung squamous cell carcinoma and lung adenocarcinoma were significantly different (P < 0.05). The sensitivity and specificity of CK5/6 in malignant pleural effusion caused by lung squamous cell carcinoma were 92.86% (95% CI: 0.64, 0.99) and 89.58% (95% CI: 0.77, 0.99); those of P63 were 91.67% (95% CI: 0.60, 0.99) and 72.73% (95% CI: 0.54, 0.86); those of TTF-1 were 87.18% (95% CI: 0.77, 0.93) and 90.63% (95% CI: 0.74, 0.98); those of CK7 were 94.23% (95% CI: 0.83, 0.98) and 75.00% (95% CI: 0.41, 0.93). The AUC of ROC curve for TTF-1 and CK7 in the diagnosis of lung adenocarcinoma were 0.821 and 0.774 respectively; correspondingly, those of the CK5/6 and P63 in the diagnosis of squamous cell carcinoma were 0.805 and 0.755 respectively. Conclusions The TTF-1, CK7, CK5/6, and P63 are important in guiding the diagnosis of lung adenocarcinoma and squamous cell carcinoma. Thin-Cytologic Test combined with the immunohistochemistry method is clinically useful for the pathological diagnosis and classification of malignant effusion caused by NSCLC.