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Cutaneous and subcutaneous mast cell tumors (MCTs) are common canine neoplasms characterized by variable biological behavior. Tumor-associated macrophages (TAMs) and tumor-infiltrating lymphocytes (TILs) can be effective prognostic markers in numerous human neoplasms and are increasingly investigated in dogs. The aim of this study was to characterize immune cells in canine MCTs and their relationship with histological location (cutaneous, subcutaneous) and histologic nodal metastatic status (HN0-3). Thirty-eight MCTs (26 cutaneous, 12 subcutaneous) from 33 dogs with known sentinel lymph node (SLN) metastatic status were immunolabeled for Iba1 (macrophages), CD20 (B cells), CD3 (T cells), and Foxp3 (regulatory T cells). Semiquantitative scoring of interstitial and perivascular CD3+, CD20+, and Foxp3+ cells and morphological evaluation of Iba1+ cells were performed. For each marker, the percent immunopositive area was evaluated by image analysis. All MCTs were diffusely infiltrated by Iba1+ cells and variably infiltrated by CD20+, CD3+, and rare Foxp3+ cells. Stellate/spindle Iba1+ cells were associated with HN2 and HN3 SLNs. Perivascular Foxp3+ cells, CD3+ cells, and percent CD3+ areas were increased in subcutaneous MCTs. Interstitial CD3+ cells were increased in cutaneous MCTs with HN0 SLNs. No differences in CD20+ cells were identified between cutaneous and subcutaneous MCTs and among SLN classes. MCTs were markedly infiltrated by TAMs and variably infiltrated by TILs. Stellate/spindle morphology of TAMs associated with HN2 and HN3 SLNs is suggestive of a pro-tumoral (M2) phenotype. Cutaneous and subcutaneous MCTs have different tumor-immune microenvironments, and T-cell infiltration might contribute to prevention of nodal metastatic spread of cutaneous MCTs. [ABSTRACT FROM AUTHOR]

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]

Tumour stage is a prognostic indicator for canine malignant head and neck tumours (MHNT). However, consensus is lacking on nodal staging in the absence of clinically apparent nodal disease (cN0 neck). This prospective observational study aims to determine the diagnostic accuracy of radiopharmaceutical and blue dye for sentinel lymph node biopsy (SLNB), to assess the correspondence between sentinel lymph node (SLN) and clinically expected regional lymph node (RLN) and the impact on staging of the procedure in dogs with MHNT and cN0 neck. Twenty-three dogs with MHNT and cN0 neck underwent tumour excision and SLNB guided by preoperative lymphoscintigraphy and intraoperative gamma-probe and blue dye. Diagnostic performances and detection rate were calculated. Correspondence between SLN and RLN, number of nodes excised, histopathological status of the SLN and complications related to the procedure were recorded. The mapping technique identified at least one SLN in 19/23 dogs, with a detection rate of 83%. The SLN did not correspond to the RLN in 52% of dogs. Multiple nodes were removed in 61% of dogs. At histopathology, eight (42%) dogs had SLN+, of which four differed from the RLN. Only minor self-limiting complications occurred in five (22%) dogs. Radiopharmaceutical and blue dye guidance is accurate (sensitivity 88.9%; specificity 100%) for SLNB in dogs with MHNT and cN0 and allowed the extirpation of unpredictable and/or multiple SLN with minimal morbidity. Incorporation of SLNB in the management of MHNT is desirable to correctly stage the cN0 neck, owing the unpredictability of the lymphatic drainage. [ABSTRACT FROM AUTHOR]