Osteosarcoma, or OSA, is the most common bone tumor found in dogs. This type of cancer can also occur in cats, but it is far less common. In dogs, osteosarcoma is very aggressive and tends to spread rapidly to other parts of the body, making early detection and treatment incredibly important. Here we’ll review causes and symptoms so that you’ll know what to look out for, as well as treatment options so you’ll know what to expect.
Causes of Osteosarcoma in Dogs and Cats
The causes of osteosarcoma in dogs and cats are not well understood. What we do know is that middle-aged to older large and giant breed dogs are the most widely affected.
Osteosarcoma can occur in any bone in the body, though in dogs, most tumors appear in the front limbs near the “wrist.”
Symptoms of Osteosarcoma in Dogs and Cats
The symptoms of bone cancer can be subtle, and may include lameness, swelling or a lump near the tumor site, bone or joint pain, lethargy, and loss of appetite.
Lameness is certainly the most common symptom and often the most obvious as well. A dog may experience sudden lameness (for example, following strenuous exercise or jumping off the bed) or the lameness may develop more slowly.
Diagnosing Osteosarcoma in Dogs and Cats
Many pets end up at the vet’s office after their owner notices lameness that is not resolving. The symptom is investigated with a radiograph, which will reveal a problem area if osteosarcoma is present. In order to reach a definitive diagnosis, the problem area must be biopsied. However, not all veterinarians perform this procedure; in some cases, the results of the radiograph will be suggestive enough to assume a diagnosis.
In addition, chest x-rays, blood testing, and a urinalysis will be performed to assess the pet’s overall health. In most dogs (around 90 to 95%), the tumor will have already metastasized (spread) at the time of diagnosis. Osteosarcoma tumors most commonly spread to the lungs, but this rarely shows up during testing as the metastatic tumors are initially microscopic. However because of the high incidence of metastasis, most pets are treated for it regardless of what testing reveals.
Treatment for Osteosarcoma in Dogs and Cats
Because osteosarcoma tumors are very likely to spread, the most common treatment is amputation of the affected limb followed by chemotherapy to treat existing metastasis or metastasis that can’t yet be seen. For many owners, amputation is a difficult decision, and not all pets are candidates (for example, dogs with severe arthritis in the affected limb). However amputation is a good option for many other dogs, and dogs with three legs can actually function very well.
If the dog is not a candidate for amputation, or if the owner decides that they do not want to go through with it, the only other option is palliative care. Palliative care aims only to make the animal more comfortable; it does not solve the underlying problem. Common palliative treatments include radiation therapy and drugs (analgesics) to reduce pain. Pets treated with palliative care tend to survive only 6 months before they succumb to the cancer or require euthanasia.
The prognosis for pets with osteosarcoma depends on the severity and spread of the disease as well as the treatment carried out. Pets who undergo amputation and chemotherapy tend to have a fair-to-good prognosis, and some pets are even completely cured. As mentioned above, pets that receive only palliative care survive an average of 6 months. Your veterinarian will help you determine the best course of treatment for your pet.
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