Bone Cancer in Dogs (Osteosarcoma)

Canine cancer can be a dog owners’ worst nightmare and few other cancers are as terrifying as bone cancer. Osteosarcoma is the most common form of bone cancer found in dogs, accounting for around 85% of total bone tumors.  It is aggressive, quick to spread or metastasize, and difficult to treat. Below we list the symptoms, treatment options, and outcomes of osteosarcoma in our canine companions. 

WHAT TYPES OF DOGS GET OSTEOSARCOMA?

Nobody knows why this disease happens. Unlike cancers such as melanoma, there is no real link to lifestyle or exposure. Most affected dogs usually have the following characteristics in common:

• Giant, large and medium dog breeds are more greatly affected than smaller breeds.
• Middle-aged. It is rarely seen in young dogs or in dogs older than eight or nine.
• Males show a higher incidence than females.

There is some hypothesis about metallic implants used for fracture repairs causing greater tumor existence, as well as radiation exposure from treating a previous tumor in the same area. Both need more research to confirm.

WHAT DOES OSTEOSARCOMA IN DOGS LOOK LIKE?

Since the vast majority of bone cancer tumors appear in the limbs, the first symptoms are very similar to other leg injuries or afflictions

• Mild to severe lameness that can either be acute or chronic in nature.
• Swelling associated with the lameness except in very early cases.
• Pathologic fractures, meaning fractures of the bone for no apparent reason, are not uncommon even early on.
• Loss of appetite and lethargy. Osteosarcoma is a very painful disease, so it can be fairly typical for dogs to show whole body affects.

Tumors on bones other than the limbs, such as the vertebrae, ribs or jaw, may also be painful and swelling. Vertebral tumors may also cause lameness or paralysis or other neurological effects depending on location. These types of tumors are not usually as recognizable in the early stages and therefore, symptoms can be less obvious.

Dogs with osteosarcoma that has spread to the lungs may also have difficulty breathing or exercise intolerance. This is typically later on in the disease however.

DIAGNOSING BONE CANCER IN DOGS

The first step in diagnosis is for the veterinarian to take a thorough history and perform an examination. This history should include onset and duration of the symptoms, palpation of any swellings or lameness and radiography. Any swellings or areas of pain should be radiographed for signs of osteosarcoma. The telltale radiographic sign of osteosarcoma is lysis, or eating away, of the affected bone. This lysis causes the area to be weakened, painful, and more prone to fracture.

If bony lysis is found on radiographs, follow up diagnostic tests may include:

• Histopathology or cytology of the area to determine the reason for lysis. A microscopic examination of the cells collected via a fine needle aspirate can help distinguish between infection versus cancer and what type of cancer your dog is dealing with.
• Radiographs of the chest. This will help determine if the cancer has spread to the lungs and lymph nodes. However, less than 5% of these animals will actually have visible radiographic metastasis to the lungs at the time of presentation.
• Blood work to get a full body picture. This will check on other organ systems to see if they are running up to par and able to handle any treatment decided by you and your vet.
• Commuted tomography, or CT, for a better view of the chest can be done if needed depending on treatment protocol chosen.
• Magnetic resonance imaging, or MRI, if certain treatment procedures are to be used.

TREATMENT OPTIONS FOR DOGS WITH BONE CANCER

Treatment should be attempted only after a thorough discussion with your veterinarian.  The protocol will depend on the stage of the disease, presence of metastases, your dog’s overall health, and the options available in your area or within your veterinarian’s capabilities. The most common treatment options or a combination of them are:

• Surgical amputation of the limb or tumor resection if not in the limbs
• Chemotherapy
• Radiation
• Palliative or hospice measures to keep the patient comfortable

The most common first step is amputation or bone tumor resection with or without chemotherapy. It is important to consider each case individually as some dogs with arthritis or other medical conditions will not tolerate an amputation well. Also, the location of the tumor needs to be considered as some locations, such as the skull, can be inoperable.

Another surgical option that is sometimes used is what is called a limb-sparing technique.  This procedure is reserved for those tumors that are in the limbs and are further from the body. It is used when animals or owners can not tolerate an amputation.

The procedure includes removing the affected area of the bone en bloc, or the whole section with margins. Usually this means the entire end of the bone, leaving an empty gap between the end of the resected bone and the joint. A metal plate is then inserted to support the dog’s weight when walking and a bone graft is placed in the space to encourage new bone growth and fill in the gap.

Chemotherapy and radiation are considered specialty services that most general practitioners are unable to offer. These treatments require special equipment and handling and can cause severe side effects that need to be considered before performing. There is also a great expense and usually some travel associated with these treatments.

Palliative or hospice care is reserved for later stage or highly progressive cases that will not respond well to any of the above treatments. This usually includes high potency pain killers, such as morphine, and antiflammatories, such as steroids, to help keep your dog comfortable and offer pain relief for as long as possible. Other medications may be used as well depending on the degree and location of metastases.  However, it is very important to monitor the dogs comfort throughout this care and consider whether or they are still having a good quality of life.

WHAT TO EXPECT

No matter which treatment option is chosen for osteosarcoma, the survival time is nowhere near what we want. This is again because of the aggressive nature of the cancer and its ability to spread quickly.

• Dogs with amputation alone have a median survival time of 3-4 months.
• Dogs treated with amputation and chemotherapy usually survive about a year.
• There doesn’t seem to be a difference in survival rates between amputation and limb-sparing procedures.
• Dogs left untreated have survival times that vary depending on other dog health factors and stage of the cancer. However, most survival times are less than three months.

As you can see, bone cancer is a very grim and hated disease that affects our best friends. No one wants to be on the receiving end of the diagnosis, or the giving end for that matter. It is very important to be in tune to your dog and be able to recognize the symptoms of osteosarcoma as soon as possible in order to have the longest survival time imaginable.

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