Canine multilobular osteosarcoma of the skull with metastasis

A 6-year-old crossbreed dog had recurring nodular masses on the dorsum of the head which were diagnosed as multilobular osteosarcoma. At necropsy, metastases were present throughout the lungs. Histological features of the masses included multiple islands of cartilage and bone separated by a dense fibrovascular stroma. These tumours are slow growing malignant neoplasms which may metastasize.