Intermandibular malignant mesenchymoma in a crossbreed dog.

A 12-year-old German shepherd crossbreed dog was presented with a submandibular mass that was initially diagnosed as myxosarcoma on incisional biopsy. Chest radiographs were taken for staging, and magnetic resonance imaging was performed to assess the feasibility of cytoreductive surgery before adjuvant radiotherapy. The dog underwent debulking surgery, and histology permitted reclassification of the tumour as a malignant mesenchymoma (with myxosarcomatous and osteosarcomatous differentiation). The dog was subsequently treated with four fractions of radiotherapy given at seven-day intervals and three doses of carboplatin. The dog remained stable following therapy until its condition acutely deteriorated, and it was euthanased 153 days after surgery. On postmortem examination, there were no signs of local tumour recurrence, but metastases were observed both in the thorax and in the abdomen.