Accuracy of routine cytology and immunocytochemistry in preoperative diagnosis of oral amelanotic melanomas in dogs.

Abstract

Amelanotic melanomas are one of the most common oral malignancies. The cytologic and histopathologic differentiation between amelanotic melanoma, sarcoma, and poorly differentiated carcinoma is often difficult or even impossible. The aim of this study was to assess the reliability of routine cytology and immunocytochemistry in preoperative diagnosis of canine oral amelanotic melanoma. Cytologic preparations from undifferentiated canine oral tumors were stained with Giemsa and by immunocytochemistry (ICC) using anti-cytokeratin, anti-vimentin, and anti-Melan A antibodies. The final cytologic diagnosis (including ICC) was compared to the final diagnosis based on histopathology and immunohistochemistry (IHC) results, and sensitivity and specificity of cytologic examination were determined. Final cytologic diagnoses of 38 cases agreed well with the histopathologic/immunohistochemical diagnoses, thus both specificity and sensitivity of combined routine cytology and ICC were 100% (95% confidence interval 90.8-100%). Of 32 oral tumors, diagnosis of amelanotic melanoma, sarcoma, and carcinoma was made using routine cytology and ICC. In 4 of 6 aspirates taken from lymph nodes, a preliminary diagnosis of metastatic amelanotic melanoma corresponded with the final diagnosis. Both sensitivity and specificity of routine cytology in diagnosis of amelanotic melanomas were considered moderate (66.7% and 85.7%, respectively). In conclusion, routine cytology is a reliable diagnostic method for canine oral amelanotic melanoma and metastatic amelanotic melanoma, and ICC, using anti-cytokeratin, anti-vimentin, and anti-Melan A antibodies, is an excellent supporting method for presurgical diagnosis of poorly differentiated oral malignancies in dogs.