Mast cell tumour-associated osteolysis in a Shiba dog

A 13-year-old, female Shiba dog presented with elevation of the right pelvic limb and swelling of the thigh. The right pelvic limb was severely swollen, and subcutaneous haemorrhaging was observed. Radiographs showed bone resorption in the stifle joint region. Fine-needle aspiration cytology of the stifle was consistent with a mast cell tumour. Computed tomography was performed, and the affected limb was amputated. The histo-pathological diagnosis was mast cell tumour, and the femur and tibia were found externally lysed with an internal invasion of tumour cells. The safety margins were secured, but the tumour had infiltrated the lymph nodes. Hence, the patient was treated with chemotherapy. There was no tumour recurrence or metastasis for 201 days after surgery, but the patient died. To our knowledge, no case of osteolysis due to mast cell tumour has been reported, making this a very rare case.