Aggressive chondroblastic osteosarcoma in a dog: A case report.

Canine osteosarcoma (OS) or osteogenic sarcoma is an aggressive tumor of the skeletal system, associated with a rapid progression and guarded prognosis. The osteosarcomas, mostly arise from the appendicular skeleton while axial OS (osteosarcoma of flat bones) are less reported in the majority of large breeds. This report describes complete para-clinical investigations of an aggressive chondroblastic OS involving facial flat bones with highly metastatic characterization in a large mix breed stray dog. Radiographic and computed tomography findings demonstrated an amorphous and active new bone formation, associated with the severe lytic areas in the left maxillary, orbital and zygomatic bones. Also, lots of nodular densities were distributed in all lung lobes. The cytological examination of the mass revealed individualized oval to spindle-shaped pleomorphic mesenchymal cells exhibiting many criteria of malignancy such as marked anisocytosis, anisokaryosis, prominent and multiple nucleoli. The punctate cytoplasmic vacuoles were obvious and bi-nucleated cells were frequently observed. These cells were seen in the background of an eosinophilic matrix. Histopathologic evaluation of the mass exhibited areas of osseous differentiation within the mass containing bony spicules and wavy bone formation along with the vast areas of cartilaginous differentiations with chondroblasts in lacunar spaces. Ultimately, chondroblastic OS with severe lung metastasis was confirmed and the animal was euthanized.