Micronucleus Formation and Tumour Cell Cannibalism in Effusion Cytology: Diagnostic Utility in Differentiating Benign and Malignant Effusions.

OBJECTIVE: Cytological evaluation of effusion fluids is a rapid and minimally invasive method for detecting malignancy; however, distinguishing malignant cells from reactive mesothelial cells remains challenging. This study aimed to evaluate the diagnostic utility of micronucleus scoring and tumour cell cannibalism in differentiating benign and malignant effusions. METHODS: This retrospective observational study included 100 pleural and ascitic fluid samples. Smears were prepared, stained with May-Grünwald-Giemsa, and examined by light microscopy. Micronucleus scoring was performed by counting the number of micronucleated cells among 1000 well-preserved cells in each case, according to the method described by Ganesan et al. Tumour cell cannibalism was also quantified on the cytological smears. RESULTS: Of the 100 cases, 49 were benign and 51 were malignant on histopathological examination. The mean micronucleus score was significantly higher in malignant effusions than in benign effusions (17.88 ± 4.50 vs. 2.31 ± 0.59 per 1000 cells; p < 0.02). Tumour cell cannibalism was identified in six malignant effusions and was absent in all benign effusions. Conventional cytological examination correctly identified 48 of 51 malignant cases and all 49 benign cases, yielding a sensitivity of 94.1%, specificity of 100%, positive predictive value of 100% and negative predictive value of 94.2%. CONCLUSIONS: Micronucleus scores are significantly higher in malignant effusions than in benign effusions and may provide an objective adjunct to routine cytomorphological assessment. Tumour cell cannibalism is highly specific for malignancy but occurs infrequently. Quantitative evaluation of these features may aid the diagnostic assessment of effusion cytology, particularly in resource-limited settings.