What is osteosarcoma?
Osteosarcoma (OSA) is a malignant bone tumour of mesenchymal origin β the most common primary bone cancer in dogs, accounting for 85β95 % of all bone tumours. It is aggressive and highly metastatic: at the time of diagnosis, an estimated 90 % of dogs already have microscopic lung metastases that are not yet visible on X-ray.
Breeds and risk factors
Osteosarcoma is predominantly a disease of large and giant breeds:
- Irish Wolfhound, Great Dane, Saint Bernard, Rottweiler.
- Labrador Retriever, Golden Retriever, German Shepherd, Irish Setter.
- Giant breeds have up to a 200-fold higher risk than small dogs.
- More common in males, middle-aged to older dogs (7β10 years), though Irish Wolfhounds can develop it before age 5.
The most frequent site is the appendicular skeleton: distal radius (wrist β the most common site overall), proximal humerus (shoulder), distal femur (stifle), proximal tibia. Classic teaching: "away from the elbow, close to the knee."
Symptoms
- Progressive lameness that does not improve with anti-inflammatories β the most common early sign.
- Painful, firm swelling over the affected bone.
- Severe pain, often worse at night.
- Muscle wasting in the affected limb.
- Pathological fracture in advanced disease β the tumour weakens the bone until minimal trauma causes a break.
Diagnosis
- Bone radiography: aggressive pattern (lytic destruction + "sunburst" periosteal reaction, Codman's triangle). Highly suggestive but not definitive.
- Thoracic radiographs (3 views): screen for visible lung metastases.
- CT thorax: more sensitive than X-ray for small metastases.
- Bone biopsy: confirms histological diagnosis; fracture risk, so it must be done at a specialist centre.
- Blood panel: elevated alkaline phosphatase (ALP) is a negative prognostic indicator.
Treatment
The standard protocol is surgery + chemotherapy:
- Limb amputation β the surgery of choice. Eliminates the primary tumour and pain. Dogs adapt remarkably well to three legs. Median survival with amputation alone: 4β6 months.
- Limb-sparing surgery: replaces the tumour bone segment with an implant or allograft. Only feasible at specific sites; higher complication rate.
- Adjuvant chemotherapy with carboplatin or cisplatin (4β6 cycles): targets micrometastases and prolongs survival. Median survival amputation + chemotherapy: 10β12 months; 20β25 % of dogs survive beyond 2 years.
- Palliative radiotherapy: for dogs not suitable for surgery; reduces pain without affecting the tumour.
- Palliative care: pain management (opioids, bisphosphonates, NSAIDs) as a dignified option when surgery is not pursued.
Prognosis
Prognosis is guarded given the high metastatic rate, but with combined treatment many dogs enjoy a year or more of good quality life. Favourable prognostic factors: normal ALP, no detectable metastases at diagnosis, distal radial location and good chemotherapy response.