Comparison of effusion cell block and biopsy immunohistochemistry in mesothelial hyperplasia, mesothelioma and carcinoma in dogs

Background: Determining the cause of effusions is challenging and may require biopsy. Whether cell blocks from effusions are representative of biopsies requires investigation. A previously developed immunohistochemical panel aids differentiation of hyperplastic and neoplastic mesothelium in canine biopsies, but has not been investigated in effusions.

Objectives: The study aimed to assess cell blocks as an alternative to biopsies, and determine whether immunohistochemistry helps distinguish hyperplastic mesothelium, mesothelioma and carcinoma.
Methods: Effusions and biopsies were collected from 5 dogs with mesothelial hyperplasia (group MH), 6 with mesothelioma (group M) and 5 with carcinoma (group C) and stained for cytokeratin, vimentin, WT1, desmin, GLUT1 and IMP3. Sections were scored for intensity and percentage cells stained.
Results: In paired cell blocks and biopsies, vimentin and WT1 staining were positively correlated for intensity and for percentage of cells positive, although not all paired results were identical. Intensity of IMP3 staining in cell blocks was higher in group M than C (P = .012), and WT1 higher in group MH than C (P = .020). For biopsies, intensity of WT1 was higher in group MH than C (P = .031). In group C, WT1 was negative in all cell blocks and biopsies and desmin negative in 4/5 cases.

Conclusions: Results in cell blocks and biopsies were comparable for potentially useful markers, such as WT1, which help discriminate between groups. Immunohistochemistry provided further information, although results were not always definitive. Further studies on a larger population are required.