Immunocytological detection of lymph node metastases in dogs with malignant epithelial tumours

The aim of this study was to compare immunolabelling of cytological specimens with conventional staining in the detection of metastases in lymph nodes from dogs with carcinoma. Cytological touch imprints of 161 lymph nodes from 72 dogs, as well as 50 fine needle aspirates from 23 dogs, with malignant epithelial tumours were included in the study. Immunolabelling was performed with commercially available human antibodies. Touch imprints of all lymph nodes were labelled with broad spectrum anticytokeratins AE1/AE3 and KL1. In addition, lymph node touch imprints from dogs with primary tumours that reacted positively with the specific anticytokeratins CK7 (n=104) and CK20 (n=20) were also labelled with CK7 and CK20. Fine needle aspirates of 50 lymph nodes were examined by immunolabelling with AE1/AE3. "Reference investigations" with a combination of histological and immunohistochemical methods were performed on all lymph nodes. The immunocytological detection of lymph node metastases with the broad spectrum anti-cytokeratin AE1/AE3 in imprint smears resulted in a significant increase in sensitivity (0.99 vs 0.88 [conventional stain]) and in negative predictive value (0.99 vs 0.85) (P<0.01; t-test). Micrometastases in particular were detected more readily. Specificity (0.93 vs 0.88) and positive predictive value (0.95 vs 0.90) did not differ significantly between the two techniques. Immunolabelling with KL1 was associated with lower sensitivity and negative predictive value, indicating lack of cross-reactivity of this antibody with canine epithelial cells. In fine needle aspirates the detection of lymph node metastases, especially micrometastases, was more efficient by mean of immunolabelling with AE1/AE3 than by conventional staining. The study indicated the value of immunocytological labelling for the detection of metastases in cytological specimens of canine lymph node preparations.