Updated May 30, 2024 — Sometimes, it starts with a misstep or slight limp, a small lump on the leg that becomes tender to the touch, or a dramatic, sudden fracture that sends a frantic pet parent and their dog to the emergency room.
Osteosarcoma is the most common primary bone tumor of dogs, and nearly 10,000 dogs are diagnosed with this cancer each year. Osteosarcoma accounts for 85% of all primary malignant bone tumors in dogs and tends to affect the limbs more commonly than the spine or skull. This type of cancer is excruciatingly painful and has a poor prognosis, with 50% of dogs surviving one year and 15-20% surviving two years with aggressive treatment.
Recognizing signs, understanding risk factors and knowing about treatment options can help you give your dog a better quality of life, even with a cancer diagnosis.
Risk Factors
Osteosarcoma can affect any dog at any age, but some identifiable risk factors exist. These include:
- High-risk breeds
- Boxer
- Great Dane
- Rottweiler
- Saint Bernard
- Irish setter
- Doberman pinscher
- Greyhound
- German shepherd
- Irish wolfhound
- Leonberger
- Height (which often tracks with larger breeds)
- Increased weight (another variable that can coincide with breed)
- Older age
- Dogs with longer noses (dolichocephaly) are at higher risk compared to those with shorter faces (brachycephaly)
- Dogs with chondrodysplasia (short-legged dogs) have a lower risk.
A recently published study took a different angle when looking at breed susceptibility for osteosarcoma. The research team grouped dogs based on genetic similarities rather than as individual breeds when determining risk. For example, in this study, the mastiff-terrier group (which includes boxers, golden retrievers and mastiffs) had the highest incidence of osteosarcoma. One conclusion reached by the research team was that veterinarians and owners might want to take extra care if a dog is a member of a susceptible group and has a sudden lameness.
Another ongoing debate revolves around the effect of spay/neuter timing on the incidence of OSA. Some studies suggest that earlier age at spay/neuter is a risk factor for disease, but other studies show the opposite. All agree that more research is needed, and the Foundation’s Golden Retriever Lifetime Study closely follows cases of osteosarcoma in the enrolled dogs to add critically needed data to this important question.
Newer studies suggest three distinct subtypes of osteosarcoma (fibroblastic, osteoblastic and chondroblastic), each with a different prognosis. Studies are ongoing to learn more about these subtypes as a step toward a more personalized treatment approach.
Signs/Symptoms and Diagnosis
The most common reported signs of osteosarcoma include:
- Lameness
- Swelling or “lump” growing on a limb
- Sudden bone fracture
- X-rays help diagnose osteosarcoma and rule out other common causes of lameness. Unlike bacterial or fungal infections, which can affect both bones of a particular joint, osteosarcoma does not cross a joint – this can be a tip-off that a patient has a bone tumor and not an infection.
Despite physical examination findings and X-rays suggestive of cancer, it can still be unclear if a bone abnormality is due to osteosarcoma, a different type of cancer, or another disease affecting bone, such as infection. A bone biopsy may be necessary to make a definitive diagnosis.
Treatment
The treatment of osteosarcoma almost always begins with amputation of the affected limb. Although many owners are understandably upset and concerned about amputating a limb, most dogs do very well with surgery. Because osteosarcoma is a painful disease, amputation also provides relief from unrelenting discomfort that is hard to control with pain medication.
However, the prognosis remains poor with surgery alone; 90% of dogs will die of this disease within one year if surgery is the only treatment attempted.
Limb-sparing techniques for treating osteosarcoma have steadily improved since they were first developed in the late 1980s and 1990s. Another form of limb-sparing treatment involves the careful and controlled use of radiation therapy instead of surgery. Many institutions, including researchers funded by the Foundation, are working on optimizing this form of treatment for dogs.
Chemotherapy can help prolong remissions, with some dogs living years after amputation and chemotherapy. However, these success stories tend to be the outliers, not the norm, and the odds are still poor for long-term survival. Osteosarcoma spreads quickly, usually to the lungs, and many dogs have metastases by the time of diagnosis, even if there are no apparent signs of disease spread.
Finding new treatment options is an area of intense research, with some exciting new findings.
One new therapy causing some buzz among veterinary oncologists uses the anti-hypertension medication losartan as adjunct chemotherapy for dogs with osteosarcoma. A trial in dogs with osteosarcoma spread to the lungs showed that losartan, combined with the chemotherapeutic toceranib, benefited half the dogs. More extensive studies are needed and ongoing, but this combination could help dogs suffering from osteosarcoma.
(To learn more about repurposed drugs for cancer treatment, including losartan, check out our podcast interview with veterinary oncologist Dr. Barb Kitchell)
Other teams are exploring immunotherapy, which harnesses the power of a dog’s immune system to attack and destroy cancer cells. Although immunotherapy hasn’t yet provided a “silver bullet” for osteosarcoma, it remains an active study area.
Science to Save Animals Starts with YOU
Sadly, an estimated six million dogs are diagnosed with cancer each year, including osteosarcoma, and cancer remains a leading cause of death in adult dogs. Veterinarians have limited treatment options due to a lack of funding for research focused on the many cancers that take our dogs’ lives too early.
We funded our first canine osteosarcoma grant in 1985. Since then, we’ve supported 68 research projects and awarded just over $8M to veterinary scientists worldwide to find better ways to tackle this devastating and common cancer in dogs. Our funding has led to an increased understanding of the biology of osteosarcoma, a critical step toward better diagnostics and treatments.
However, there’s more we need to learn, and we need your help.
During our Stop Cancer Furever campaign, we’re raising funds for cancer research to find answers, develop new diagnostic tests and discover new treatments to help dogs suffering from cancer.
Our friends at Petco Love and Blue Buffalo share our vision of a cancer-free future for the animals we love. Donate today, and they’ll match your gift dollar for dollar, up to $100,000, through June 30, 2024. Together, we can Stop Cancer Furever.
Will you join us in funding the science we need to save more lives?
Additional Resources:
- Foundation-funded researcher Dr. Nicola Mason featured on 60 Minutes
- Morris Animal Foundation Funds New Study to Advance Osteosarcoma Treatment
- New Study Aims to Revolutionize Osteosarcoma Treatment for Giant Dog Breeds
