Diagnostic and prognostic value of Ki67 proliferation fraction in serous effusions

The Ki67 proliferation rate of mesothelial cells was determined in 20 effusions due to malignant mesotheliomas and in 20 non-neoplastic effusions, to investigate if this marker may be useful to identify neoplastic mesothelioma cells and if there is a correlation between proliferation rate and survival time. Using the ABC-method, effusions were immunostained and the marker Ki67 was evaluated quantitatively. Ki67 proliferation fraction showed rates from 2.3% to 70% in malignant mesothelioma cells and from 1.8% to 25.5% in reactive mesothelial cells. A significant difference was found (p=0.05) between those two groups. Assuming a threshold at 26%, a sensitivity of 25% and specificity of 100% resulted. Yet, due to its low sensitivity this marker seems not to be useful for differential diagnosis. Plotting surviving period against Ki67 proliferation fraction a correlation was observed which was not significant. Long term survivors (>28 month) showed proliferation rates below 3.8%. Unexpectedly a highly significant difference (p=0.001) between Ki67 proliferation rates of mesothelial cells from patients with malignant tumors other than mesothelial origin (7.0% to 25.5%) and mesothelial cells of patients without any malignant disease (1.8% to 16.3%) were observed. Setting a threshold at 10% for identification of a malignant disease, a sensitivity of 77.8% and specificity of 90.9% resulted.