Osteosarcoma In Cats And Dogs

Written by Shula Berg BVSc CertAVP(GSAS) GPAdvCert(SASTS) MRCVS
Clinically reviewed by Elizabeth McLennan-Green BVM&S CertAVP(SAM) MRCVS

Table of Contents

- Overview
- Symptoms
- Diagnosis
- Treatment
- Outlook

Osteosarcoma (OSA) is the most common tumour affecting the bones in dogs and cats, with up to 85% of bone tumours being this type. OSA usually presents primarily in one bone, and the majority of cases are found in the limbs. The most common sites for OSA are the wrist, shoulder, and around the knee. Much less commonly, OSA can affect the spine, jaw, ribs or skull.   

Osteosarcoma typically affects middle-aged to older dogs, but can occur in dogs of any age. It is significantly more common in large or giant breed dogs, especially Great Danes, Dobermanns, German Shepherds, Golden Retrievers and Rottweilers. OSA affects male and female dogs equally. In the vast majority of cases, no underlying cause for OSA is found. However, bone tumours can be induced by chronic inflammation, and sometimes will occur in places where there has previously been a fracture or infection of the bone. 

What are the symptoms of Osteosarcoma?

In the early stages of disease, dogs may show no symptoms of OSA. Eventually, the tumour will cause pain and dogs will start to limp on the affected leg. Sometimes, this is preceded by a mild trauma, such as a slip or fall, which aggravates the already fragile bone. Swelling may be visible if the affected leg is compared to the other side. 

Less commonly, bone tumours are found when the bone becomes so weak it breaks. This will cause a sudden, non-weight bearing lameness, sometimes with a visible deformity of the limb. This is known as a pathological fracture, and often happens without an obvious trauma or impact. 

Which tests are used to diagnose Osteosarcoma?

In the majority of dogs, suspicion of a bone tumour is raised on clinical examination. When the affected leg is examined, the bone may feel thickened or swollen, and is often painful when pressure is applied. If there is a pathological fracture, it may not be possible to know there is a tumour present from examination alone, as all fractures are painful. 

X-rays are required to make a diagnosis of a bone tumour. There are a number of changes that are known to be characteristic of bone tumours, and the presence of these in a large-breed dog with compatible symptoms is usually enough to make a diagnosis. Occasionally, especially if the tumour is not advanced, changes on x-ray can be inconclusive and a second opinion or repeat imaging may be recommended. 

The only way to definitively diagnose Osteosarcoma is with a biopsy of the abnormal bone. If significant changes to the bone are present, there is a risk of pathological fracture occurring during the biopsy process. As mentioned previously, OSA accounts for 85% of canine bone tumours, so it is often assumed that this is the tumour present. A biopsy is more often recommended in cases with less advanced changes, or where we are uncertain of the diagnosis. However, your vet will advise the best option in your dog’s case. 

How is Osteosarcoma treated?

Treatment of Osteosarcoma is challenging, as it is a very aggressive type of tumour, and often spreads before it is diagnosed. Up to 90% of dogs will have some metastases (spread) at the time of diagnosis, most commonly in the lungs. X-rays of the lungs are very poor at identifying metastases, as they will not identify very small abnormalities. The ideal method to assess for micro-tumours in the lungs is a CT scan of the chest. However, given the high likelihood of metastases, this is not recommended for every case, and may depend on which treatment options are being considered. 

Unfortunately, there is no effective treatment available to resolve the primary tumour in first opinion practice, so the majority of treatment options involve amputation of the affected limb. Often, a biopsy is not performed at the time of diagnosis, but analysis of the tumour is performed after amputation.   

The bone tumour itself is often very painful, so amputation can be used as a sole treatment to increase comfort. In these cases, the average survival after surgery is 3-4 months, with 90% of dogs surviving less than a year. Amputation is often more traumatic for us as owners than it is for our pet, and the majority of pets will be completely healed within two weeks of surgery. Most dogs will cope well on three legs, though the larger the dog, the more difficult they may find it. Your vet will be happy to advise on how your pet may cope with an amputation. 

Limb-sparing surgery, in which the tumour is removed and the bone supported with metal implants, is available at a small number of specialist centres. This is an alternative to amputation, predominantly for patients who are anticipated to struggle on three legs due to concurrent orthopaedic or neurological problems. Limb-sparing surgery has increased risks of infection and tumour recurrence when compared to amputation, with a longer post-operative recovery, but may be an option for some dogs. 

Chemotherapy can be used after amputation to try and reduce metastases elsewhere in the body. This often prolongs survival but does not achieve a cure. Various protocols are used, most will involve multiple intravenous infusions over a period of weeks to months. Chemotherapy doses used in animals are significantly lower than those used in humans, so we do not see the same degree of side-effects. However, there are human safety and cost considerations that mean chemotherapy is not suited to every pet. Dogs who have amputation and chemotherapy often survive for around a year, with 20% of cases alive two years after diagnosis. 

Due to the inability to achieve a complete cure with any treatment options, some owners feel that treatment is not the right decision for their pet. In these cases palliative treatment can be used, consisting primarily of pain relief to reduce the discomfort from the primary bone lesion. Palliative radiotherapy has been prescribed for OSA, with around 70% of dogs showing increased comfort for 2-4 months. However, there are few places in the UK offering this. Newer technology, such as stereotactic radiation, may offer fewer side-effects than conventional radiation therapy. 

What is the outlook for pets with Osteosarcoma?

Sadly, the prognosis for dogs with Osteosarcoma is guarded, as all dogs are likely to eventually succumb to the disease. Although treatment with surgery and chemotherapy can extend survival times to over a year, many owners feel this is not the right decision for their pet. As a result, a large number of dogs with Osteosarcoma are put to sleep shortly after diagnosis due to the pain of the tumour. Deciding whether to treat Osteosarcoma is often a difficult decision, and your vet will be happy to talk through the options and guide you to what is right for you and your dog. 


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Page last reviewed: 24th April 2024

Next review due: 24th April 2026