LAUSR

ABSTRACT Background Subcutaneous mast cell tumours (ScMCTs) have been traditionally associated with a good prognosis, with low rates of recurrence and metastasis. Objectives This study aims to describe the clinical presentation, outcome, and prognostic factors in dogs diagnosed with ScMCTs and treated with a curative‐intent approach. Methods Clinical and histopathological data were retrospectively collected from dogs diagnosed with ScMCTs after undergoing curative‐intent surgery and complete staging between 2018 and 2023 in a single institution. Adjuvant and neoadjuvant therapies were allowed. The study's endpoints were the disease‐free interval (DFI) and disease‐specific survival time (DSST). Variables, including location, histopathological description, clinical stage, infiltrative behaviour, atypia, Darier's sign, surgical margins, mitotic count (MC) >4 in 10 high power fields (HPF), nodal status, and chemotherapy after surgery, were evaluated as potential influences on DFI and DSST. Results Thirty‐two cases were included. Lymphadenectomies were performed in 18/32 (56.3%), and nodal metastases (early or overt) were documented in 12/32 (37.5%). The median follow‐up was 405 days (range 79–1312). In 9/32 (28.1%), the disease progressed, and 7/32 (21.9%) died of ScMCT‐related causes. The median DFI and DSST were not reached at 1312 days. The overall 1‐year and 2‐year survival rates were 80% and 70%, respectively. Patients presenting with Darier's sign, MC >4 in 10 HPF, and those who received chemotherapy had a higher risk of dying from the disease (hazard ratios of 14.9, 5.8 and 8.4, respectively). Conclusions Our results suggest that despite the overall good long‐term prognosis of ScMCTs, they may exhibit a higher metastatic rate at presentation than previously reported. Additionally, patients with Darier's sign or a high mitotic count may be associated with a poorer prognosis.