Immunocytochemical panel for distinguishing between adenocarcinomas and reactive mesothelial cells in effusion cell blocks

The aim of our study was to determine the value of a panel that consisted of one epithelial marker (MOC‐31) and two mesothelial markers (D2‐40 and calretinin) for distinguishing between reactive mesothelial cells (RMCs) and adenocarcinomas (ACs) in effusion fluids. A total of 118 cell block specimens from pleural and peritoneal effusions, including 88 ACs and 30 benign effusions with RMCs were stained with antibodies against MOC‐31, D2‐40, and calretinin. MOC‐31 membranous activity was observed in all samples from ACs, regardless of the primary tumor site. All benign effusion samples with RMCs were negative for MOC‐31. All benign effusion samples with RMCs exhibited membranous staining for D2‐40, and one AC case had focal reactivity for D2‐40. Almost all benign effusions reacted positively with calretinin. Staining was noted in both the cytoplasm and the nucleus in the majority of cases. Scattered tumor cells had weak calretinin positivity in two AC cases. Background RMCs in AC effusions were consistently positive for D2‐40 and calretinin. In general, D2‐40 identified more RMCs than calretinin. The staining combination of positive for MOC‐31 and negative for D2‐40 or calretinin were 100% specific and 99% sensitive for ACs. Our data suggest that immunohistochemical studies performed on cell blocks with MOC‐31, D2‐40, and calretinin were useful in the differentiation between ACs and RMCs. D2‐40 was a more sensitive marker for RMCs than calretinin. Diagn. Cytopathol. 2009. © 2009 Wiley‐Liss, Inc.