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

Abstract

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.