WHAT IS OSTEOSARCOMA?
Osteosarcoma (OSA) is the most common primary bone tumour, which most commonly affects one of the limbs (appendicular OSA) but can also in other regions of the skeleton (e.g. skull) and non-skeleton tissues (e.g. organs, skin, and mammary glands.)
Appendicular OSA is usually a disease of large to giant breeds of dogs.
WHAT ARE THE SIGNS OF OSTEOSARCOMA?
OSA can be found in any bone at any location. Lameness and localised limb swelling are the most common signs when the tumour affects a leg.
WHAT TESTS ARE NEEDED?
X-rays of the affected area are required to differentiate primary bone tumours from other orthopaedic diseases. Other primary bone tumours and also bone infections may look the same and cannot be differentiated by x-rays alone. Biopsy or aspirates of the region is required for definitive diagnosis and to differentiated OSA from other bone tumours and also non-cancerous causes of bone changes (e.g. bone infection).
Staging of the disease with assessment of the local lymph node, lungs (by x-rays or CT) and other bones is required to assess for metastasis (spread) of the tumour prior definitive treatment as it affect treatment options and prognosis is metastasis is found.
In addition bloods and urine testing is important to evaluate general health status and ability to tolerate surgery and chemotherapy.
WHAT TREATMENT IS NEEDED?
There are different options for therapy and these include palliative-intent or curative-intent options.
Palliative-intent care- Palliation is indicated for dogs with metastatic disease, or when owners do not want to pursue more aggressive treatment options. Palliative therapy is geared toward management of pain and lameness associated with the primary bone tumour but does not improve survival time. Pain relief medications and sometimes drugs to reduce bone turnover are the cornerstone for the palliative management of dogs with primary bone tumours. Radiotherapy therapy is also effective for palliation of dogs with primary bone tumours however is not currently available in WA. Limb amputation may also be used as a palliative measure to improve pain, but does not improve survival.
Curative-intent care – Curative-intent care required different types of therapy used together to improve quality and quantity of life expectancy. This involves both surgery and chemotherapy together.
Limb amputation is required for local control of the tumour. Many owners have concerns how their pet will deal with amputation, however, experience has shown that even dogs with concurrent issues such as osteoarthritis, obesity, and body size are rarely impact on pet’s ability to cope. Dogs with neurologic disease or severe clinical osteoarthritis are exceptions, and palliative management or limb-sparing surgery can be discussed these cases.
Chemotherapy is required in addition to amputation or limb-sparing surgery to treat cancer cells that have already metastasised (spread) but are no evident on staging. Surgery, unless combined with chemotherapy, is considered palliative. Chemotherapy without surgery does not provide a survival benefit over other palliative techniques. Chemotherapy is usually started at the time of suture removal after amputation. Different chemotherapy protocols are available for the use of treatment of OSA, and studies have not shown differences in survival times among the different protocols. And choice of protocol is usually based on possible side effects and cost in each patient.
WHAT IS THE PROGNOSIS?
Metastatic disease is the most common cause of death or euthanasia in dogs with appendicular OSA after definitive treatment. Lung and skeletal sites are most frequently involved. The life span for dogs with OSA treated with limb amputation alone is 103 to 175 days with 47% to 52% dogs still alive at 6 months. The life span for dogs treated with surgery and chemotherapy is improved to 235 to 366 days, with a 33% to 65% alive at 12-months and 16% to 28% at 24-months.
Poor prognostic factors in dogs with OSA include age less than 7 years or greater than 10 years, body weight greater than 40 kg, large tumour size, certain tumour location, increased preoperative alkaline phosphatase (ALP) activity that fails to normalize within 40 days of surgical removal of the tumour, high tumour grade, and presence of metastatic disease.