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Simple Summary: Cytological evaluation of lymph nodes (LN) during staging of canine Mast Cell Tumors (MCTs) is a hot topic. While histology is currently the gold standard of LN evaluation, cytology would have the advantage of in vivo investigation that allows for the planning of a therapeutical approach. However, at present, LN cytological examination and interpretation needs to be standardized. In the present work, the significance of the nodal mast cell number in dogs with and without MCT has been investigated, comparing different counting methods and different sample preparation techniques. Our results suggest that, while counting methods and sample preparation technique do not influence MC count, the nodal MC number can discriminate between metastatic and non-metastatic LNs, but fails to distinguish between metastatic and possibly metastatic LNs. Cytological evaluation of lymph nodes (LN) in canine cutaneous mast cell tumors (MCT) has a key role in MCT staging. However, cytological discrimination between metastatic and reactive LNs is debated and diagnostic criteria inconsistent. The aim of this study was to retrospectively quantify nodal mast cells (MCs) in non-oncological (NOD) and MCT-bearing dogs (MCTBD), using different sample preparation techniques, to evaluate the significance of the MCT number. Cytological specimens from NOD-LNs (10 fine-needle aspirates—FNAs) and MCTBD-LNs (10 FNAs, 10 scrapings, 10 touch imprints) were evaluated. MCTBD-LNs were grouped in: non-metastatic, possibly-metastatic, and metastatic based on current literature criteria. MCs were counted in 4, 8, and 20 high-power-fields, and over 500, 1000, and 2000 total cells. MCs were significantly more numerous in MCTBD-LNs than in NOD-LNs and in "metastatic" samples than in "non-metastatic". There was no significant difference between "metastatic" and "possibly metastatic" samples. Sample preparation techniques did not influence these results. A negative correlation between MCs number and sample cellularity was observed. Results were confirmed regardless of the counting method applied. MCs counting per se cannot distinguish possibly metastatic and metastatic cytological samples. Sample preparation technique and the counting method applied seem to have no influence on cytological quantification of nodal MCs in MCTBDs. [ABSTRACT FROM AUTHOR]

Background: Cytopathology is a minimally invasive and convenient diagnostic procedure, often used as a substitute for histopathology to diagnose and characterize lymphoma in dogs. Objectives: Assess the diagnostic performance of cytopathology in diagnosing lymphoma and its histopathological subtypes in dogs. Animals One‐hundred and sixty‐one lymph node samples from 139 dogs with enlarged peripheral lymph nodes. Methods: Based only on cytopathology, 6 examiners independently provided the following interpretations on each sample: (a) lymphoma vs nonlymphoma; (b) grade and phenotype; and (c) World Health Organization (WHO) histopathological subtype. Histopathology and immunohistochemistry (IHC) findings were used as reference standards to evaluate diagnostic performance of cytopathology. Clinical, clinicopathologic, and imaging data also were considered in the definitive diagnosis. Results: Classification accuracy for lymphoma consistently was >80% for all examiners, whereas it was >60% for low grade T‐cell lymphomas, >30% for high grade B‐cell lymphomas, >20% for high grade T‐cell lymphomas, and <40% for low grade B‐cell lymphomas. Interobserver agreement evaluated by kappa scores was 0.55 and 0.32 for identification of lymphoma cases, and of grade plus immunophenotype, respectively. Conclusions and Clinical Importance: Cytopathology may result in accurate diagnosis of lymphoma, but accuracy decreases when further characterization is needed. Cytopathology represents a fundamental aid in identifying lymphoma and can be used as a screening test to predict grade and phenotype. However, these results must be confirmed using other ancillary techniques, including flow cytometry, histopathology, and immunohistochemistry (IHC). [ABSTRACT FROM AUTHOR]