Axial osteosarcoma develops in the bones of the skull, jaw, spine, ribs, or pelvis — collectively known as the axial skeleton — and accounts for about 15% of all canine bone cancers. It arises from the same bone-forming cells as appendicular osteosarcoma, but its behaviour and outlook vary considerably depending on the precise location. Tumours in the jaw (mandible) tend to spread less frequently and carry a relatively favourable prognosis when surgically removed, while vertebral (spinal) and pelvic tumours are more challenging to treat and carry a poorer outlook. As with limb osteosarcoma, large and giant breeds are most commonly affected. Treatment planning focuses on achieving complete surgical removal where anatomy allows, which directly determines outcome.