Bone Cancer in Dogs – Canine Osteosarcoma

December 29, 2020

The most common primary bone tumor in dogs is osteosarcoma (osteo= bone, sarcoma = cancer).  This is especially true for large and giant breeds. Osteosarcoma (OSA) is most often seen in middle aged to older dogs.  But it has also been reported in younger dogs (1-2 years old).

Osteosarcoma is a locally aggressive tumor, characterized by painful bone destruction where the tumor grows. It commonly affects the limbs of dogs with the forelimbs being affected twice as often as the hind limbs. The distal radius (wrist) and proximal humerus (upper part of the arm) are the most frequently affected sites. OSA can occur in other skeletal areas (i.e. skull, pelvis, vertebrae) and extraskeletal parts of the body. Osteosarcomas are also highly metastatic tumors (high likelihood of spread) predominantly to the lungs.

Clinical signs

The most common presentation of canine OSA is lameness of the affected limb (leg) and at times, a noticeable swelling may be seen at the tumor site. The lameness may be intermittent initially and temporary improvement may occur with symptomatic therapy. Some dogs may present to the veterinarian due to a fracture caused by the weakening of the affected bone.

As the disease and pain progresses, other clinical signs may be seen including exercise intolerance, loss of appetite, weight loss and even aggression. Other clinical signs may be seen and will vary depending on the primary site and involvement of underlying structures. If pulmonary metastasis (spread into the lungs) is present, some patients may also experience respiratory signs.

Diagnostics

The initial workup includes bloodwork (complete blood cell count and serum biochemistry profile), for complete health assessment and radiographs (x-rays) of the affected limb. Radiograph of the thorax (chest x-rays) is the most critical element of clinical staging. An abdominal ultrasound should also be considered, especially in older pets, to provide information that could potentially influence treatment recommendations. Other possible diagnostic tools include a bone scan look for other areas of bone involvement.

In many instances, radiographs (x-rays) of the affected legs are often highly suggestive of the diagnosis of bone cancer with osteosarcoma being the most common bone tumor. At times, fine needle aspirate or bone biopsy of the affected area can be considered for further confirmation of the diagnosis using heavy sedation or general anesthesia.

Staging diagnostics are essential to determine the tumor type, extent of the pet’s cancer and the overall general health of the pet, all of which may influence the treatment recommendations.

Treatment

Our goal here at The Cancer Center at AVCC is to provide our clients with variable treatment options to help their pets live the longest and best quality of life possible despite of their cancer diagnosis.

• Surgery

Definitive treatment for appendicular osteosarcoma typically involves surgical amputation of the affected leg followed by systemic chemotherapy. In some cases, limb-sparing procedures may be possible.

Making the decision to amputate your pet’s leg can be very emotional and overwhelming. Our goal is to support you through this process and help ease fears towards amputation. Amputation is one of the best treatment options we can provide to eliminate pain associated with bone tumor. One of the main concerns our owners have regarding amputation is the uncertainty of how their pets will adapt after the procedure, both physically and mentally. Most dogs do remarkably well following an amputation and can do virtually everything that 4-legged dogs can do.

It is important to know that dogs with severe arthritis in the unaffected limbs, or weakness due to neurologic disease may not be candidates for amputation. In these cases, other treatment options can be explore to help ease their pain and maintain a good quality of life.

Please make sure to check the websites below for more information on videos of three legged dogs that could further assist you with your decision making process.

www.tripawds.com and www.bonecancerdogs.org

• Limb-sparing procedures

In some cases, a limb-sparing surgical procedure can be done as an alternative to surgery. This is mainly done in dog with bone tumors of the distal radius (lower forelimb). The purpose of a limb sparing surgical procedure is to remove the primary tumor while providing a pain free functional limb. This option requires intense follow-up care to help decrease the rate of complications. This surgical procedure is mainly performed at veterinary university settings.

• Stereotactic radiation therapy (SRT)

Another alternative to amputation is a more advanced, highly accurate type of radiation therapy called stereotactic radiation therapy. This type of radiation therapy uses high doses of radiation to the tumor while minimizing damage to surrounding healthy tissues. Chemotherapy is still indicated to prevent or delay the risk of metastasis (spread).

• Chemotherapy

As we have mentioned previously, canine osteosarcoma is an aggressive, locally invasive and highly metastatic cancer (high rate of distant spread mainly to the lungs). Therefore, chemotherapy is commonly used as an adjunct to local therapy (i.e. amputation) to slow the rate of metastasis.

Several chemotherapy agents have been used for the treatment of canine osteosarcoma. In our clinic, the most commonly used chemotherapy drug is called carboplatin and is typically given every 3 weeks for 6 doses. Chemotherapy in our pets is generally very well tolerated and they have a great quality of life while undergoing therapy. Some dogs do experience mild, self-limiting side effects such as depressed appetite, nausea, occasional vomiting, and diarrhea for a few days. Less than five percent of dogs will experience severe side effects requiring hospitalization. If severe side effects occur, the dosages of these drugs can be reduced in the subsequent treatments.

Once chemotherapy has been completed, we recommend frequent monitoring for evidence of metastasis which is done primarily with chest x-rays.

Palliative treatment

• Radiation therapy

Palliative radiation therapy (RT) is very effective at providing pain relief when amputation is not an option. RT can be applied to the tumor in 2-4 doses depending on the protocol elected. It can provide comfort and improved limb function in 70-80% of treated dogs. Palliative radiation therapy can be given in conjunction with other palliative treatment modalities including bisphosphonates.

• Bisphosphonates

These drugs decrease bone destruction, which in turn helps control the pain and bone damage caused by the bone tumor. They have been shown to improve cancer-related bone pain in dogs and humans. There are two commonly used bisphosphonates drugs, zoledronate and pamidronate. Treatment is given intravenously as a drip over several minutes to hours depending upon the drug used. This treatment is repeated every 3 to 4 weeks.

• Oral pain management

Pain management is critical to dogs with osteosarcoma due to the painful nature of the disease. Multimodal pain management is needed in order to alleviate pain and provide comfort. These medications typically include non-steroidal anti-inflammatory medications, opioids and neuropathic pain relievers. It is important to understand that there is a limit to how much pain relief can be achieved using this treatment modality.

Prognosis

Prognosis for dogs with osteosarcoma is based on many factors but mainly depends on the severity and spread of the disease and on the treatment elected. The median survival time following amputation and chemotherapy is closer to a year with 10-20% of patients surviving to 2+ years.

Rest assured, we are equipped with the expertise and compassion to assist you with decision-making and help your dog achieve a comfortable life and improved survival if diagnosed with this condition.

The Cancer Center at AVCC is located in South Florida in Broward County.
8920 W. State Road 84,
Davie, Florida 33324
954-500-8387

The Cancer Center at AVCC offers the following oncology services:

Diagnostic tests including:

• Fine needle aspirates/cytology
• Bone marrow aspirates
• Bone biopsies
• Incisional and punch biopsies
• Personalized genomic testing

Treatment:

• Traditional chemotherapy (intravenous/intracavitary)
• Metronomic chemotherapy
• Targeted chemotherapy
• Immunotherapy
• Palliative care and pain management
• Hospice counseling
• Nutritional counseling and referral
• Referral for pet radiation therapy

For more on cancer treatment for your pet, see our Comprehensive Guide to Pet Cancer Care.

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