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Canine cutaneous mast cell tumours (cMCTs) of the pinna have been associated with an aggressive biological behaviour, although data remain scarce. The knowledge acquired over the past years on histologic gradings, and the value of lymph node (LN) staging, may help in better characterizing this anatomical presentation. The first aim was to describe the frequency, location, and histologic appearance of LN metastases in cMCT of the pinna. A second aim was to evaluate prognosis. Medical records of dogs with cMCT of the pinna, that underwent tumour and sentinel (SLN) or regional LN (RLN) excision, were reviewed. The influence of potential prognostic variables on time to progression (TTP) and tumour‐specific survival (TSS) was investigated. Thirty‐nine dogs were included: 19 (48.7%) had Kiupel high‐grade (K‐HG) and 20 (51.3%) had low‐grade (K‐LG) MCTs. Eighteen (46.1%) dogs underwent SLN mapping: the superficial cervical LN was at least one of SLN in 17 (94.4%) cases. Twenty‐two (56.4%) dogs had LN metastases; the superficial cervical LN was always involved. On multivariable analysis, only K‐HG was associated with increased risk of progression (p =.043) and tumour‐related death (p =.021). Median TTP and TSS were 270 and 370 days in K‐HG, respectively; these were not reached in dogs with K‐LG tumours (p <.01). cMCTs of the pinna are often K‐HG and are also associated with a higher frequency of LN metastasis; however, we confirmed the independent prognostic value of histologic grading. A multimodal treatment may lead to favourable long‐term outcome. Moreover, the superficial cervical LN is most often the SLN. [ABSTRACT FROM AUTHOR]

In canine cutaneous mast cell tumours (cMCTs), histologic grade and clinical stage are the most important prognostic factors, with high‐grade tumours and metastatic lymph nodes (LNs) significantly influencing the evolution of disease. However, it is uncertain whether histologic grade and clinical stage should be given equal weighting value in patient prognostication and management. Dogs with low‐ and high‐grade cMCTs and at least one overtly metastatic sentinel LN undergoing standardized treatment, consisting of surgical excision of the cMCT, lymphadenectomy and chemotherapy, were retrospectively included. The aim was to determine whether, at the same clinical stage, histologic grade retained prognostic relevance. Sixty dogs were included: 26 had a high‐grade cMCT tumour and 34 had a low‐grade cMCT. Median follow‐up was 367 days (range, 187–748) in the high‐grade group, and 1208 days (range, 180–2576) in the low‐grade group. Median time to progression was significantly shorter in the high‐grade group than in the low‐grade group (214 days versus not reached; p <.001), as well as tumour‐specific survival (545 days versus not reached; p <.001). On multivariable analysis, a high histologic grade and incomplete margins retained prognostic significance for both tumour progression and tumour‐specific death. In dogs with cMCT and at least one overtly metastatic LN undergoing multimodal treatment, histologic grade significantly correlated with outcome. Overall prognosis was not unfavourable, even in the high‐grade group, further supporting that a multimodal therapeutic approach, addressing primary tumour and sentinel LN, should be offered. Whether chemotherapy should be incorporated in the therapeutic planning of low‐grade cMCTs remains to be defined. [ABSTRACT FROM AUTHOR]