Investigation of the utility of lymph node fine-needle aspiration cytology for the staging of malignant solid tumors in dogs.

Abstract

Fine-needle aspiration cytology (FNAC) of lymph nodes (LNs) is routinely used for staging canine malignant solid tumors, but studies evaluating its efficacy are limited. The primary objectives of this study were to evaluate the sensitivity/specificity of FNAC and the significance of nondiagnostic FNAC when staging canine malignant tumors. A secondary objective was to determine the prevalence of multiple nodal metastases. Lymph nodes draining malignant solid tumors assessed with FNAC and histopathology were included. The sensitivity/specificity of FNAC was determined for LNs with diagnostic FNAC, using histopathology as the gold standard. The proportion of nondiagnostic FNAC and associated histopathologic prevalence of metastasis were determined. Among the tumors with multiple LNs assessed, the prevalence of multiple nodal metastases was determined. The sensitivity of FNAC (194 LNs) was 67% for sarcomas, 100% for carcinomas, 63% for melanomas, 75% for mast cell tumors, and 100% for other round cell tumors. The specificity varied between 83% and 96%. Nondiagnostic FNAC was reported in 25% of LNs sampled (65/259), most of which were nonenlarged and/or difficult to access, and 20% of which were metastatic on histopathology. When several LNs were assessed (88/189 tumors), the prevalence of multiple nodal metastases was 24%. Histopathologic LN evaluation cannot be robustly substituted with FNAC when staging selected canine solid tumors. When a diagnostic FNAC is elusive, the histopathologic assessment remains ideal. Finally, staging should not always be limited to the assessment of a single LN.