Clinical, pathological and prognostic features of surgically excised cutaneous and subcutaneous digital and distal limb mast cell tumours in dogs

Objective To evaluate clinical, pathological and prognostic features and outcomes of dogs with surgically excised cutaneous and subcutaneous digital or distal limb mast cell tumours. Materials and Methods Medical records between 2014 and 2024 were reviewed, and signalment, clinicopathological testing, tumour location, recurrence, complications and histological characteristics were recorded. Additionally, progression‐free interval and overall survival time were evaluated. One hundred and fifteen client‐owned dogs with mast cell tumour admitted to two academic institutions were included. Results Surgical complications occurred in 38% of dogs with surgical site infection and incisional dehiscence most common. Local recurrence occurred in 23% of dogs overall, with completely excised tumours having 10% recurrence, narrowly excised 20% and incompletely excised 35%. Higher recurrence rates occurred with incomplete surgical margins, mitotic count >5 and histologically high‐grade mast cell tumours. The median progression‐free interval was significantly longer for wide excision (2270 days) compared to marginal excision (888 days). The overall survival time was 7 years for all dogs overall, was not reached for low‐grade mast cell tumours and was 3 years for high‐grade mast cell tumours. The progression‐free interval and overall survival time were affected by tumour grade but not lymph node status. Clinical Significance The behaviour of canine mast cell tumours affecting the digits and distal limb was affected primarily by tumours grade. Recurrence rates were highest in dogs with high‐grade mast cell tumours, incomplete surgical resection and a mitotic count of >5. The outcome with surgical excision is excellent. Future studies are needed to further evaluate the effects of adjuvant chemotherapy, metastatic lymph node status and lymph node extirpation in high‐grade mast cell tumour cases.