IMMUNOPROFILE IN EFFUSION CYTOLOGY

BACKGROUND: Cytology has a crucial role for diagnosing pleural and abdominal effusions. A prompt accurate diagnosis has both prognostic and therapeutic significance. However, cell morphology alone is not always sufficient to formulate such a diagnosis. In human medicine, immunocytochemistry of effusion cytology has now standardized procedures that provide reliable insights into various diagnostic dilemmas. OBJECTIVE: To describe the method of immunocytochemistry in effusion cytology and to estimate the value of a panel of markers in identifying cells in canine and feline effusions. MATERIALS AND METHODS: Human, feline and canine mesothelial cells were isolated in culture. Western‐blot (WB) analysis was used to ascertain antibody cross‐reactivity for all the markers, with the exception of HBME‐1. Forty‐four cytospined or smeared effusion specimens from dogs and cats with a cytological diagnosis of reactive effusion or malignancy of non‐hematopoietic origin were stained with a standard panel of Vimentin, Cytokeratin (CK) AE1/AE3, CK 5/6 and HBME‐1 as mesothelial cell markers; desmin as mesothelial cell malignancy marker; and CK7/CK20 as a marker of metastasis. Malignancy was confirmed by histologic evaluation; non‐malignant conditions were confirmed by follow‐up. Sensitivities, specificities and predictive values were calculated. RESULTS: The WB analysis confirmed the specific crossreactivity of the human antibodies for canine and feline proteins in mesothelial tissue. No significant differences were found between canine and feline results. Vimentin/cytokeratin coexpression had a sensitivity of 79% and a specificity of 92%, HBME‐1 had 89% sensitivity and 23% specificity, and CK5/6 had 26% sensitivity and 100% specificity for mesothelial cells. Desmin had only 20% specificity for benign mesothelial cells, while CK7‐/CK20+ had a specificity of 79% and sensitivity of 30% for metastatic cells on effusions. CONCLUSION: Immunocytochemistry can be applied in effusion samples, and valuable results can be obtained. The most useful marker, with the highest overall accuracy for the identification of mesothelial cells in effusion, is the Vim/CK coexpression, being CK5/6 the more specific and HBME‐1 the more sensitive antibody. Desmin is not useful for discriminating between benign and malignant mesothelial cells. The coordinate expression of CK7‐/CK20+ has not proved to be useful on the identification of metastatic cells on effusions.