Osteosarcoma is a form of bone cancer that occurs in dogs, commonly affecting the long bones of their legs. It is more prevalent in large and giant breed dogs. Many dog owners worry about their dogs being stricken with cancer, and a diagnosis can be extremely difficult to face. Understanding osteosarcoma can help you acquire a swift veterinary diagnosis so that you can determine the most appropriate course of treatment and give your dog supportive care as well as the best possible quality of life.
What Is Osteosarcoma?
Osteosarcoma is the most common type of bone tumor in dogs. It can affect any bone in the body but most commonly occurs in the limbs, beginning as a tumor in one of the long bones of a leg. The tumor tends to grow from the inside of the bone, displacing healthy bone. In addition to being painful, the bone develops a "moth-eaten" appearance and becomes weak. Fractures can easily occur in the area of the tumor.
Metastasis is common in osteosarcoma. This type of cancer easily spreads to other areas of the body, especially the lungs.
Symptoms of Osteosarcoma in Dogs
The first sign of osteosarcoma in dogs is usually discomfort in the affected bone. If a limb is affected, the dog may limp or hold up the affected limb, indicating pain. At first, this may seem like a minor injury. However, it typically will not improve with treatment and rest.
Limping or favoring a leg is commonly a sign of injury. Less frequently, these behaviors may indicate a more serious problem. If your dog's discomfort does not ease with time and rest, its symptoms should be carefully evaluated by a veterinarian. As osteosarcoma progresses, the affected area may become swollen and tender to the touch. The bone may eventually fracture without any actual injury. Fractures of cancerous bone will not heal with treatment the way normal breaks do.
Causes of Osteosarcoma
The exact cause of osteosarcoma in dogs is not known. Large and giant breed dogs seem to have a predisposition to this type of cancer. In addition, there may be a hereditary component. Osteosarcoma usually occurs in middle-aged and senior dogs, but younger dogs can occasionally be affected as well (especially young giant breed dogs).
Diagnosing Osteosarcoma in Dogs
If you notice lameness or swelling in one or more of your dog's limbs, be sure to visit your veterinarian as soon as you can. Lameness that does not respond to traditional treatments (pain relievers, anti-inflammatory drugs, rest) is concerning and warrants additional diagnostic testing. Your vet will likely recommend radiographs (x-rays) of the affected area.
Osteosarcoma may be presumptively diagnosed based upon radiographic evidence. Bony tumors often have a mottled appearance that can be seen. However, a tissue sample is needed to make a definitive diagnosis. Your veterinarian may be able to perform the additional tests. Or, you may be referred to a veterinary specialist like an orthopedic surgeon or oncologist.
A bone biopsy may be performed to collect a cross-section of bone at the site of the suspected tumor. However, taking a sample of bone may further weaken the compromised bone and lead to fractures. Some vets prefer to do a needle biopsy and take a smaller piece of tissue from within the bone. This may be enough tissue for a pathologist to diagnose osteosarcoma.
This is the next diagnostic step. Staging is a series of tests done to look for metastasis (spread) of cancer. Chest radiographs are generally the first step as osteosarcoma commonly spreads to the lungs first. Staging may include an abdominal ultrasound to look for cancer and other changes to the abdominal cavity and organs. All dogs should have lab testing (blood chemistry, complete blood count, and urinalysis) performed to assess organ function and analyze cells.
Treatment of Osteosarcoma in Dogs
There are a few treatment options for dogs with osteosarcoma. The right option for your dog will depend on the location of the tumor and the severity of metastasis.
This is the first step for dogs with osteosarcoma in a long bone of the limb. It may sound like an extreme step to remove an entire limb, but the pain from osteosarcoma tends to be much worse than the pain and recovery of amputation.
Most dogs adjust well to life with three limbs. Dogs feel so much better after having the source of pain removed that they tend to bounce back quickly. Most dogs can run, jump, and play better than before. One exception is dogs with arthritis or other orthopedic conditions in one or more limbs. These dogs might not be the best candidates for amputation.
This is typically recommended when osteosarcoma is found in an inoperable area or when the dog is a poor candidate for amputation. Dogs receive a short course of radiation to the tumor. This radiation therapy can significantly reduce pain for several months, improving the dog's quality of life for a time. Palliative radiation may be repeated every few months if the pain returns. Dogs are often treated concurrently with special medications to control pain and minimize bone destruction.
This may be attempted in dogs when their limbs cannot be amputated. This procedure typically involves the removal of the primary tumor and bone grafting. Dogs will need chemotherapy in conjunction with limb-sparing surgery.
This is often needed to treat metastasized cancer. It is also necessary when dogs have limb-sparing surgery. Dogs will generally need to visit an oncologist weekly to get chemotherapy injections or infusions for six months or longer. Fortunately, the side effects of chemotherapy are often relatively mild in dogs.
It's important to have an in-depth conversation with your veterinary oncologist so you can make the right treatment decisions for your dog. The oncologist will be able to provide the most up-to-date statistics about recovery and survival so you can make informed decisions.
Prognosis for a Dog with Osteosarcoma
A dog's prognosis largely depends on the stage of the osteosarcoma and the available treatment options. If amputation is possible, and the cancer has not spread to other parts of the body, then the dog may heal and regain a happy, active lifestyle. Senior dogs, or those with more advanced disease, will have a harder time regaining health and will need targeted treatments, as recommended by a veterinary oncologist, as well as a great deal of comfort and loving support from their owners. If a dog is given a negative prognosis, then quality-of-life care is of utmost importance for the dog and the people who love it.