METHODS: A total of 108 pleural, peritoneal, and pericardial effusions/washings diagnosed as unequivocally reactive (n = 41) and metastatic carcinoma (n = 67) by cytomorphology over 18 months were reviewed. Among the metastatic carcinoma cases, 54 were adenocarcinoma and others were squamous cell carcinoma (n = 1), carcinosarcoma (n = 1), and carcinoma of undefined histological subtypes (n = 11). Cell block sections were immunostained by EZH2 (Cell Marque, USA). The percentages of EZH2-immunolabeled cells over the total cells of interest were calculated. Receiver operating characteristic (ROC) curve analysis was performed to determine the optimal cut-off score to define EZH2 immunopositivity.
RESULTS: A threshold of 8% EZH2-immunolabeled cells allows distinction between malignant and reactive mesothelial cells, with 95.5% sensitivity, 100% specificity, 100% positive predictive value, and 93.2% negative predictive value (p < 0.0001). The area under the curve was 0.988.
CONCLUSION: EZH2 is a promising diagnostic biomarker for malignancy in effusion cytology which is inexpensive yet trustworthy and could potentially be used routinely in countries under considerable economic constraints.