What Is Osteosarcoma?
Osteosarcoma (OSA) is a malignant tumour arising from bone-producing cells called osteoblasts. It is the most common primary bone tumour in dogs, accounting for approximately 85 per cent of all skeletal malignancies in the species. Osteosarcoma is an aggressive cancer: it is locally destructive, causing significant bone pain and structural weakening, and it spreads rapidly — most commonly to the lungs — even when the primary tumour appears to be confined to a single site at the time of diagnosis.
Whilst the diagnosis carries a poor long-term prognosis, advances in veterinary oncology over recent decades have meaningfully extended survival times and improved quality of life for affected dogs.
Breeds Predisposed to Osteosarcoma
Giant and large breeds are disproportionately affected, and body size is considered the most significant risk factor for osteosarcoma. Breeds with the highest documented risk include:
- Greyhound
- Rottweiler
- Scottish Deerhound
- Irish Wolfhound
- Great Dane
- Saint Bernard
- Leonberger
- Dobermann
Middle-aged to older dogs are most commonly affected, with a peak incidence between seven and ten years of age, though younger large-breed dogs can also develop the disease. Male dogs are affected slightly more often than females. Neutering has been associated with altered risk in some breeds, particularly Rottweilers, though the relationship is complex and not fully understood.
Most Common Location: The Distal Radius
Osteosarcoma most commonly affects the long bones of the limbs — specifically the metaphyses, the regions of bone adjacent to the growth plates. The most frequently affected site in dogs is the distal radius (the lower end of the foreleg, just above the wrist). Other common sites include the proximal humerus (shoulder), proximal tibia (below the stifle), and distal femur (above the stifle). The skull, jaw, ribs, and spine can also be affected, though less frequently.
A useful mnemonic used in veterinary oncology is that osteosarcoma affects bones "away from the elbow and near the knee" — reflecting the predilection for the distal forelimb and proximal hindlimb.
Clinical Signs
The presenting signs of osteosarcoma are primarily related to bone pain and structural compromise:
- Progressive, often severe lameness on the affected limb — typically worsening over days to weeks
- Visible swelling at the tumour site, which may feel warm to the touch
- Pain on palpation of the affected bone
- Reluctance to bear weight or complete non-weight-bearing lameness
- Pathological fracture — a fracture occurring through tumour-weakened bone during normal activity — in advanced cases
Because the tumour destroys normal bone architecture, the structural integrity of the affected limb is severely compromised. Pathological fractures are a particular concern and represent a veterinary emergency, as the limb becomes non-functional and pain becomes extreme.
Diagnosis
Veterinary assessment begins with X-rays of the affected limb. Osteosarcoma has characteristic radiographic features: a mixed pattern of bone destruction and abnormal bone production, often with a "sunburst" appearance and lifting of the periosteum (the bone's outer layer). However, X-rays alone cannot definitively distinguish osteosarcoma from other bone conditions including bone infection (osteomyelitis) or other tumour types.
A definitive diagnosis requires a bone biopsy — a sample of tissue from the tumour that is examined histologically by a veterinary pathologist. Biopsy can be performed under general anaesthesia using a Jamshidi needle (a hollow cutting needle) or via an open surgical approach. The procedure carries a small risk of pathological fracture, particularly in severely affected bones, and this must be weighed against the diagnostic benefit.
Staging — determining whether the disease has spread — involves chest X-rays and ideally CT scanning of the thorax. Because osteosarcoma metastasises early and via the bloodstream, approximately 90 per cent of dogs are estimated to have microscopic pulmonary metastases at the time of diagnosis even when the chest appears clear on imaging.
Treatment: Amputation and Chemotherapy
The standard of care for appendicular (limb) osteosarcoma in dogs involves two components: local control of the primary tumour and systemic treatment to target metastatic disease.
Amputation
Surgical amputation of the affected limb achieves immediate and complete local control of the tumour and, most importantly, provides excellent pain relief. Dogs adapt remarkably well to life on three legs — particularly if they are not excessively overweight — and most owners report that their dog's quality of life improves significantly in the weeks following surgery as the chronic bone pain is eliminated.
Limb-sparing surgery (removing the tumour whilst preserving the limb) is an alternative in selected cases, particularly for distal radius tumours, but carries higher complication rates and is typically only available at specialist oncology centres.
Chemotherapy
Amputation alone, without systemic treatment, is associated with a median survival time of approximately four months. The addition of chemotherapy — most commonly platinum-based protocols using carboplatin or cisplatin, with or without doxorubicin — extends median survival to around ten to twelve months. Approximately 20 to 25 per cent of dogs treated with amputation and chemotherapy survive beyond two years.
Chemotherapy protocols in veterinary oncology are generally less intensive than those used in human medicine and are designed to minimise side effects whilst maximising anti-tumour activity. Most dogs tolerate veterinary chemotherapy well and maintain an acceptable quality of life during treatment.
Palliative Care Options
For dogs in whom surgery is not an option — due to owner choice, the dog's age or concurrent health problems, or financial constraints — palliative care aims to manage bone pain and maintain quality of life for as long as possible.
- Palliative radiation therapy can provide meaningful pain relief in a proportion of dogs, typically requiring a course of several treatments. Stereotactic radiosurgery (SRS), available at a small number of UK referral centres, can deliver high-dose targeted radiation in fewer sessions.
- NSAIDs and opioid analgesics are the mainstay of medical pain management
- Bisphosphonate drugs (such as pamidronate) may help reduce bone pain and slow local bone destruction
- Palliative care without surgery carries a median survival of one to two months, though individual cases vary considerably
Facing the Diagnosis
An osteosarcoma diagnosis is devastating, and the decisions facing owners — regarding surgery, chemotherapy, and ultimately quality of life and timing of euthanasia — are never easy. Veterinary oncologists and specialist referral centres in the UK can provide detailed guidance tailored to the individual dog's situation, helping owners make informed choices that prioritise their pet's welfare above all else.
Written by Sarah Bennett, animal health writer at ForPetsHealthcare.