Osteosarcoma and Your Pet
- Osteosarcoma is a type of cancer that primarily affects the bone.
- It tends to occur in older, large- to giant-breed dogs and is relatively rare in cats.
- Most tumors occur in the limbs; clinical signs may include pain, lameness, swelling at the tumor site, lethargy (loss of energy), and loss of appetite.
- A bone biopsy, or tissue sample, is required for a definitive diagnosis.
- Other diagnostic tests may include radiographs (x-rays), a complete blood count (CBC), a chemistry panel, urinalysis, and possibly a computed tomography (CT) scan.
- Treatment may include surgical removal of the affected bone, radiation therapy, and possibly chemotherapy or other medications.
What Is Osteosarcoma?
Osteosarcoma is a type of malignant (cancerous) tumor that primarily affects the bone. Primary osteosarcomas arise from tissues within the bone itself, while secondary osteosarcomas spread to the bone from other locations. Osteosarcoma is the most common primary bone tumor in dogs but is relatively rare, and usually less aggressive, in cats. This type of cancer generally affects older, large- or giant-breed dogs, but it can occur at any age.
Most tumors occur in the limbs, but osteosarcomas may also appear on the ribs, spine, and skull, and even in tissues such as the spleen and mammary glands. Although the exact cause of this cancer is unknown, previous trauma at the tumor site may be a contributing factor.
What Are the Clinical Signs of Osteosarcoma?
The signs of osteosarcoma depend on the location of the tumor. Dogs with limb tumors may show evidence of pain and lameness, often with a gradual onset. There may be a firm swelling at the tumor site. Occasionally, the tumor can cause the bone to weaken and break, which is called apathologic fracture.
Skull tumors may result in seizures or facial deformities. Pets with rib tumors may have difficulty breathing if the tumor is impinging on, or has spread to, the lungs. Spinal tumors may result in impaired movement. Pets may show general signs of lethargy (lack of energy) and loss of appetite.
How Is Osteosarcoma Diagnosed?
Your veterinarian may recommend a number of diagnostic tests:
- Radiographs (x-rays): Radiographs of the bone are useful to help distinguish tumors from other problems, such as fractures and bone infections, and to determine the extent of bone involvement. Your veterinarian may also recommend chest radiographs to check for signs that the tumor has spread to the lungs, a common site for metastasis (the spread of cancer).
- Computed tomography (CT) scan: Compared with traditional radiographs, a CT scan may provide more detail of the bone and the lungs.
- Bone biopsy: A small sample of the bone is required to make a definitive diagnosis.
- Complete blood count (CBC), chemistry profile, and urinalysis: These tests may provide information to help the veterinarian determine a prognosis and whether the pet is a good candidate for chemotherapy, if needed.
Treatment and Prognosis
Your veterinarian may refer you to a veterinary oncologist (a cancer specialist) for more information about the options available for your pet.
Unfortunately, most osteosarcomas have already metastasized (spread) to the lungs by the time of diagnosis. Although some chest radiographs may show obvious lung tumors, the lesions can often be microscopic and unseen on radiographs.
Because of the high risk of lung metastasis and the associated poor prognosis, many pet owners choose palliative therapy, which does not cure but can relieve pain and improve the pet’s quality of life.
Treatment usually begins with surgical removal of the bone, when possible. This usually means a leg amputation for pets with limb tumors. In some cases, a bone graft may be attempted to help spare the limb, but there are often limitations and complications with these procedures. Most pets are able to get around surprisingly well with three limbs. Still, amputation alone rarely cures the disease.
For tumors in locations where surgical removal is difficult, or if the owner chooses to forgo surgery, radiation therapy and pain medications may relieve pain and temporarily help the pet feel better.
In dogs that show no signs of metastasis, surgery followed by chemotherapy can help improve the pet’s life expectancy.
As with all types of cancer, early diagnosis and treatment can improve the prognosis for your pet. That’s why it’s important to have your veterinarian examine your dog any time you notice signs of lameness or swelling, especially in the limbs.