The cell tube block technique and an immunohistochemistry panel including Wilms tumor 1 to assist in diagnosing cavitary effusions in dogs and cats.

Abstract

Cell blocks and immunohistochemistry (IHC) are increasingly recognized as being complementary tools for cytologic diagnostics, especially for neoplastic diseases. The study aimed to evaluate the utility of cell tube block (CTB) IHC for refining the diagnosis of effusions in dogs and cats. Cavitary effusions (n=25) from dogs and cats classified by cytology as reactive, neoplastic, borderline (suspicious of neoplasia), and chylous were studied. CTB sections were stained with H&E, and immunostained with PAX-5, CD3, pancytokeratin (CK), vimentin, and Wilms tumor 1 protein (WT1) antibodies, according to the cytologic diagnoses. A histologic case series of confirmed normal, reactive, and neoplastic mesothelium and several different carcinomas were included to test the utility of WT1 as a marker of mesothelial cells. CTBs had a layered appearance with reduced background staining. CD3 and PAX5 immunolabeling allowed immunophenotype assessment in all of the lymphoma cases. In carcinomatous effusions, neoplastic cells were CK-positive, WT1-negative, and vimentin-negative (except for two cases). Wilms tumor 1 protein was positive in the nuclei of normal, reactive, and neoplastic mesothelial cells, and ovarian carcinomatous cells. Other carcinomas and lymphomas were negative. CTBs are valuable tools to assist in making a diagnosis of cavitary effusions in dogs and cats, and WT1 is a promising marker to differentiate mesothelial from carcinomatous cells.