Monoclonal antibody MOC-31 reactivity as a marker for adenocarcinoma in cytologic preparations.

It has been shown previously that detection of the epithelial membrane antigen using the mouse monoclonal antibody MOC-31 has diagnostic utility in the distinction between mesothelioma and metastatic carcinoma in body fluids. The current immunohistochemical study confirmed the effectiveness of MOC-31 as a marker for adenocarcinoma from a broad range of primary sites in body fluid cytology prepared as paraffin sections of cell blocks. The authors evaluated 112 cell blocks for MOC-31 immunoreactivity, including 17 mesotheliomas, 86 metastatic adenocarcinomas from various sites, and 9 control fluids from patients with nonneoplastic conditions. Membranous reactivity for MOC-31 was observed in 86 of 86 samples (100%) of metastatic adenocarcinoma, regardless of the specific primary site. Sixteen of 17 mesothelioma samples were negative. In all but 1 sample of adenocarcinoma, > 90% of tumor cells present showed reactivity, and the staining intensity consistently was strong. Staining of scattered, morphologically benign mesothelial cells was observed in nine samples but did not interfere with interpretation. On the basis of the staining profile, MOC-31 represented an effective marker for metastatic carcinoma in cell block preparations and may aid in distinguishing between benign and malignant mesothelial cells in these tumors.