Proliferative index using Ki-67 index in reactive mesothelial versus metastatic adenocarcinoma cells in serous fluid

BACKGROUND: The cytological diagnoses of serous effusions are usually made by routine cytomorphology with certainty. However, overlapping cases sometimes exist between reactive mesothelial and adenocarcinoma cells. We tried to evaluate the diagnostic utility of proliferative index using a Ki-67 monoclonal antibody in distinguishing between reactive mesothelial cells and adenocarcinoma in serous effusions. MATERIALS AND METHODS: Paraffin blocks and H and E stained slides of peritoneal and pleural fluid cell blocks were retrieved from cytology archive of Alzahra Hospital, Medical University of Isfahan, between 2006 and 2010, from among 1025 slides which were screened to ascertain their appropriate diagnoses. Among of these 80 paraffin-embedded cell blocks, 40 cases for each reactive and adenocarcinoma groups were selected. The proliferative index was calculated by using the Ki 67 monoclonal antibody against nuclear proteins. RESULTS: The mean ages of the patients in the reactive mesothelial and adenocarcinoma groups were 60.58 and 58.45 years, respectively. The gender distribution for the malignant group included 23 cases (%57.5) of females and 17 cases (42.5%) of males. This ratio for reactive group included 14 cases (35%) and 26 cases (65%). The mean of Ki-67 index in adenocarcinomatous cells was 17.15 (SD=15.11) and in reactive mesothelial cells was 3.58 (SD= 3.59) (P=0.001). We consider to using the proliferative marker of Ki-67 on benign and malignant lesions revealed 12% as cut off level. The means of Ki-67 index according to serousal spaces were included: Pleura: 10.56 (SD= 13.06) and peritoneum: 10.03 (SD= 12.78), (P=0.9). CONCLUSION: Ki-67 index is useful immunostaining panel for differentiation of mesothelial and adenocarcinoma cells in malignancy like ovarian carcinoma that sometimes mimics mesothelial morphology.