A primary bone tumor, osteosarcoma is one of the five most frequently diagnosed types of cancer in dogs. Research has found correlations between these tumors and a dog’s weight and height.
What is it?
Osteosarcoma (OS), the most common canine bone cancer, accounts for 85 percent of all skeletal tumors, or roughly 25,000 cases annually in the U.S. Biologically aggressive, it tends to arise in the distal radius of the forelimb (above the carpus or “wrist”), the tibia/fibula of the hindlimb as well as in the femur. However, OS can also occur in other bones and is sometimes seen in the vertebrae and pelvis.
According to a report presented by a pet insurance company at the 2016 AVMA conference, “Disease prevalence starts to climb in late middle age, peaking from age eight to 11, after which prevalence declines in step with the typical lifespan for large and extra-large dogs. Gender does not appear a significant risk, although male dogs are slightly more affected than females.”
Signs and symptoms.
Sudden lameness without an obvious cause, swelling and pain can be indicators of OS. As pain increases, the dog may become irritable and less willing or able to move around or exercise. OS-weakened bones are prone to fractures, which is often when the cancer is discovered. By the time it’s diagnosed, it may have metastasized to the lungs, which makes treatment more challenging.
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How is it diagnosed?
To diagnose a malignant bone tumor, X-rays are the first test of choice. On an X-ray, OS will give the affected bone the appearance of being moth-eaten—or lytic, in vet-speak—due to the loss of normal bone tissue. Because other, but far less common, conditions can also cause this appearance, to reach a definitive diagnosis, the next step is usually a fine-needle aspirate or a biopsy; both are done while the dog is sedated.
If OS is confirmed, the vet will stage the cancer to determine how advanced it is. Bloodwork, urinalysis, lung X-rays and an abdominal ultrasound are usually involved. If enlarged lymph nodes are found, additional biopsies may be needed.
How is it treated?
Because osteosarcoma is fast-moving and highly likely to metastasize, the recommended treatment for bone tumors found in the leg involves amputation of the affected limb followed by chemotherapy. However, in some cases, amputation is not a viable choice.
According to “Osteosarcoma in Dogs,” a 2002 paper written by Wendy Brooks, DVM, DAVBP, and revised in 2019, “For most patients, there is one tumor on a leg and no visible tumor spread in the lungs. These are the patients with the best potential results and they are good candidates for amputation. Patients with a lot of arthritis in the other legs or with tumor spread evident in the chest already are probably not candidates for amputation and it may be more appropriate to keep the leg and simply relieve the pain with radiotherapy.”
Other options may also be suggested, depending on the tumor’s location and type. In all cases, the treating veterinarian will focus on relieving pain and doing as much as possible to stop or slow down the cancer’s spread.
ELIAS cancer immunotherapy (ECI), a recently developed experimental treatment approach, was used in a study initiated in 2017 by researchers at the University of Missouri College of Veterinary Medicine. The goal of this first-of-its kind study was to develop a “patient-specific, precision-medicine treatment” for bone cancer in dogs. Ultimately, they were able to create a personalized vaccine from the dog’s OS that—unlike chemotherapy—targeted cancer-specific cells and left normal cells untouched.
In this study, the entire treatment protocol was completed in eight weeks rather than the many months required for conventional chemotherapy. According to the report in the Journal of Veterinary Internal Medicine, for 14 dogs treated with ECI, the median survival was 415 days, and five dogs survived longer than 730 days. All of these dogs had surgical limb amputation prior to the immunotherapy, but none received chemotherapy.
Research like this is part of something called comparative medicine. Using resources created by evolving technology, scientists look for similarities and differences in canine and human cancers that will lead to better ways to prevent, diagnose and treat the disease in both. (The One Health initiative, for example, promotes collaboration and expertise integration among physicians, veterinarians and research scientists.) For OS, that involved studying its genetic profile in both species; researchers found the profiles to be indistinguishable.
While OS isn’t as common in people as it is in dogs, it accounts for about 3 percent of childhood cancers. Early limb-sparing techniques and novel treatment combinations were practiced on dogs in order to optimize them for use with children, and vice-versa. In limb-sparing, rather than amputation, the section of bone affected by the tumor is removed and replaced by a graft from a bone bank; sometimes, the remaining bone can be regrown via bone transport osteogenesis.
Are certain breeds predisposed?
Less genetic diversity exists in many breeds as a result of selective breeding for desired traits, such as appearance or physical stature. The unintended result is that certain breeds now carry a higher genetic risk for certain diseases and cancers. Genetic risks associated with canine OS have been particularly well studied. Large- and giant-breed dogs—particularly the Irish Wolfhound, Greyhound, Akbash, St. Bernard, Leonberger and Rottweiler—are the most commonly affected. Bone Cancer Dogs, an online support group for owners of dogs diagnosed with OS, has a list of OS-specific clinical trials and other in-depth information.