Osteosarcoma in Dogs

Disagled dog three legs smiling
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Osteosarcoma is a form of bone cancer that occurs in humans and dogs. Cancer is something that worries many dog owners. Understanding the disease can help you give your dog the best care and quality of life after a terrifying cancer diagnosis.

What is Osteosarcoma in Dogs?

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. In rare cases, osteosarcoma can occur in non-bony tissues, like muscles or organs.

Osteosarcoma typically affects the long bones of limbs. The tumor tends to grow from the inside of the bone, replacing the healthy bone with cancerous bony growth. In addition to being painful, the bone becomes "moth-eaten" and 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.

Signs 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 will limp or holding up the affected limb. At first, it may seem like a minor injury. However, it typically will not improve with treatment and rest.

In time, the affected area may become swollen and tender to the touch. The bone may eventually fracture without any actual injury. These fractures will not heal with treatment the way normal fractures do.

Causes of Osteosarcoma in Dogs

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 be affected as well (especially young large and 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.

Radiography

Osteosarcoma may be presumptively diagnosed based upon radiographic evidence. Bony tumors often have a mottled appearance that can clearly be seen. However, a tissue sample is needed to make a definitive diagnosis. Your veterinarian may be able to perform the additional tests needed. Or, you may be referred to a veterinary specialist like an orthopaedic surgeon or oncologist.

Biopsy

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.

Staging

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.

Amputation

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. It's much easier than it is for humans as dogs do not have the emotional attachment to their limbs that a human would. They do not experience concerns about the social stigma of amputation. Plus, they feel so much better after having the source of pain removed that they tend to bounce back quickly. Most dogs are able to run, jump, and play better than before. One exception is dogs with arthritis or other orthopaedic conditions in one or more limbs. These dogs might not be the best candidates for amputation.

Palliative radiation

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.

Limb-sparing surgery

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.

Chemotherapy

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 milder in dogs than they are in humans.

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.