Much like humans, dogs are often victims of cancer. Osteosarcoma is the most common form of bone cancer in dogs. While this cancer can be found in any canine, the larger breeds such as Mastiffs, Great Danes, and Rottweilers are most often affected. Bone cancer can also occur in cats, but it is very rare. Osteosarcoma is extremely aggressive and has a tendency to quickly spread to other tissues in the body, including the lymph nodes and lungs. While this cancer can occur in any bone in the body, the most common place for it to originate is in the legs.
The first symptom of bone cancer in dogs is usually a very subtle lameness or limp. Since this symptom is also common with degenerative joint disease (osteoarthritis), osteomyelitis (bone infection) or soft tissue trauma, including ligament or tendon injury, osteosarcoma is often misdiagnosed as it occurs less frequently, but initially looks the same as other common diseases.
The second symptom of osteosarcoma, which occurs very quickly (often within days), is swelling at the initial bone cancer site. The animal will begin to avoid putting weight on the affected limb. This swelling is very sensitive to the touch and for good reason. At the heart of the swelling, the bone is being destroyed by the cancer. This process is extremely painful, often to the point that the dog will not even put the foot of the affected limb on the ground. As the destruction from cancer progresses, bone fractures can occur.
By the time osteosarcoma is diagnosed, cancer has usually spread to other parts of the body. What clinically distinguishes osteosarcoma from other conditions is the rate at which it progresses and the high level of pain the dog experiences. Unlike other disorders that typically respond well to medications, because osteosarcoma is so very aggressive and extremely painful, the pain caused by this condition will not be helped by the medications generally used for pain and inflammation.
Diagnosis of osteosarcoma is based on the animal’s history, clinical signs, location of pain and swelling. Radiographic findings in the early stage of the bone cancer can be subtle, but very quickly, significant destruction of bone by the cancer can be seen on X-ray. Bone biopsies may be used to rule out other forms of cancers (such as chondrosarcomas) and infections. Other imaging such as a CT scan can also be helpful. Radiographic imaging of the chest can determine if the cancer has spread to the lungs.
While there are treatment options for osteosarcoma, the long-term prognosis is usually very poor. These options range from palliative care to amputation of the affected limb, followed by chemotherapy. The palliative care approach centers on the control of pain. There are combinations of narcotic and NSAIDS (nonsteroidal anti-inflammatory drugs) that mitigate the pain. Radiation therapy of the tumor site is available locally and this can significantly reduce the pain and slow the progression of the disease, but this therapy requires multiple doses of radiation to the tumor site and multiple anesthesia procedures to deliver the therapy. A more aggressive treatment approach involves amputation of the affected limb, followed by chemotherapy (carboplatin) to address cancer that has spread to the lungs.
Most dogs do really well with amputation and adapt quickly to having three legs. The chemotherapy can provide up to a year and a half of remission and these dogs live a very good quality of life with this approach. The heartbreak of this disease is that it cannot be cured and will eventually take these big and noble companions of ours from us. If your pet is diagnosed with this cancer, your veterinarian can guide you through those options. Your vet may be able to also recommend other owners have been down this path with their pet and would be willing to share their journey with this disease so you can make the best decision for you and your furry companion.
Originally published September 2016 in the Lake Norman Citizen.