IMMUNODETECTION OF SIALOSYL-TN (MUCINASSOCIATED ANTIGEN) ON MESOTHELIAL AND CARCINOMATOUS CELLS IN SEROSAL CAVITY EFFUSIONS

Background – Discrimination of malignant cells from reactive mesothelium in body cavity effusions is a diagnostic problem in some cases. In an attempt to resolve this problem, several accessory techniques have been tried without general acceptance. Sialosyl-Tn (STn) is a mucin carbohydrate-associated antigen, which represents an aberrant glycosylation product of cellular mucin carcinomas. This antigen may sparsely be detected in normal epithelial cells such as goblet cells of small and large intestinal mucosa, gallbladder, urinary bladder, salivary glands, and basal cells in normal laryngeal stratified epithelium; besides, it is frequently expressed in dysplastic epithelium and epithelial carcinomas. We investigated the STn monoclonal antibody for its clinical utility as an isolated stain to distinguish metastatic carcinomatous cells from benign mesothelium. Methods – In this study, cell block materials from the serosal cavity fluids of 76 cases (48 with malignant and 28 with nonmalignant effusions) were immunostained for detecting STn. Specimens were retrieved from the archives of the pathology departments of the teaching hospitals of Shaheed Beheshti University of Medical Sciences, Tehran, Iran from March 2000 to February 2001. Results – Strong immunoreactivity was noted in 42 (95%) and negative staining was observed in 2 (4.5 %) of the 44 carcinoma cases. Benign effusions showed no strong staining but weak response was seen in 5 (18%) of the 28 benign cases. No immunoreactivity was noted in the 4 noncarcinomatous malignant effusions. The diagnostic value indexes of STn immunostaining test were as follows: specificity: 100%, sensitivity: 95%, positive predictive value: 100%, negative predictive value: 93%, and accuracy rate: 92%. Conclusion – This method is of great value in discriminating metastatic carcinomatous cells in body cavity effusions. STn immunostaining can also be used to differentiate carcinomatous from noncarcinomatous malignant effusions.