Value of cytokeratins and calretinin in the differentiation between reactive mesothelial cells and malignant epithelial cells in cell block preparation

ABSTRACT

Malignant epithelial cells can be difficult to distinguish from reactive benign mesothelial cells in cytological smears prepared from body fluid effusions. Calretinin and cytokeratin 5/6 are valuable markers in the immunohistochemical distinction between malignant mesothelioma and adenocarcinoma in tissue sections. However, there is limited and conflicting data regarding their utility in the differential diagnosis between reactive benign mesothelial cells and malignant cells in cytologic material. The aim of the current work is to evaluate the efficiency of IHC staining of cairetinin, CK5/6, CK7, CK20 and TTF-1 in the distinction between reactive mesothelial cells and metastatic adenocarcinoma and the prediction of origin of primary carcinoma in cell blocks prepared from ascitic and pleural effusions. Formalin-fixed paraffin-embedded cell block preparations of 20 cytologic fluids were stained immunohistochemically for monoclonal antibodies to cairetinin, CK5/6, CK7, CK20, TTF-1 and CD68. Mesothelial cells showed positive immunoreactivity to calretinin and CK5/6 [100%], and CD68 [30%] while they were totally negative to CK7, CK20, and TTF-1. In contrast, malignant epithelial cells [in all studied cell block preparations] were negative to cairetinin, CK5/6 and CD68 while 50% were immunopositive to CK7, 34% to CK 20, and 15% to TTF-1. Cell block preparation is an excellent method for immunohistochemical staining of cytologic specimens. Calretinin and CK5/6 are valuable markers in the identification of reactive mesothelial cells. The use of an immunohistochemical panel of antibodies to calretinin, CK5/6, CK7, CK20, and TTF-1 is useful in the differential diagnosis between reactive mesothelial cells and metastatic adenocarcinoma in cytologic cell block preparations