Bone Tumors in Dogs and Cats

Skeletal tumors can occur in dogs and cats.

The incidence of skeletal tumors is markedly lower in cats than in dogs. Notable differences in disease characteristics exist between dogs and cats. In dogs, skeletal tumors most commonly affect the distal radius, proximal humerus, distal femur, or proximal tibia, whereas in cats, skeletal tumors are evenly distributed between appendicular and axial sites.

Skeletal tumors can be primary, secondary metastatic, or invasive from adjacent soft tissue structures. The most common primary bone tumor is osteosarcoma, accounting for over 80% of bone tumors in dogs and over 50% in cats (1, 2). Less frequently identified tumors include chondrosarcoma, fibrosarcoma, and hemangiosarcoma.

Clinical signsof skeletal tumors include lameness, bone swelling, and an acute, nontraumatic pathological bone fracture.

Radiography reveals osteolysis, proliferation, and soft tissue swelling; thoracic radiography should be performed to delineate metastatic masses (see osteosarcoma radiograph). Bone biopsy using a Michele bone trephine or Jamshidi biopsy needle is imperative to confirm the diagnosis.

Osteosarcoma, radiograph, dog

Image

Courtesy of Dr. Ronald Green.

Treatment for malignant bone tumor includes surgical intervention, such as limb amputation; chemotherapy with carboplatin, cisplatin, or doxorubicin; and sometimes radiation therapy. Palliative care to decrease pain and discomfort can be provided with oral NSAIDs, opioids, or radiation therapy.

The prognosis depends heavily on the tumor type, treatment approach, and metastatic status.

For osteosarcoma in dogs, most untreated dogs survive only 1–2 months due to pain or fractures.​ With amputation alone, median survival is 4–6.5 months. ​Amputation plus chemotherapy increases median survival to 9–12 months. Tumors in the mandible or scapula have the best prognosis (approximately 18 months survival); limbs are intermediate (approximately 11 months), and spine/skull worse (approximately 6 months), ​Most dogs ultimately die from pulmonary metastasis, and high serum ALP, proximal humerus location, and young age are negative indicators (2).

Feline osteosarcoma has a much less aggressive biological behavior than osteosarcoma in dogs. Most cats treated with aggressive surgical resection (amputation) have median survival times ranging from 2 to 4 years, with a substantial number experiencing multiyear disease-free intervals (3, 4). ​

Other malignant skeletal tumors (eg, chondrosarcoma, hemangiosarcoma, fibrosarcoma) in dogs and cats carry a prognosis that is generally variable but usually better than osteosarcoma. Chondrosarcomas, the second most common primary bone tumor in dogs, have median survival times of 1–3 years after wide surgical excision because they are slower to metastasize.

Other sarcomas (hemangiosarcoma, fibrosarcoma) tend to have a more aggressive course, but depending on location and completeness of excision, some dogs and cats can achieve several months to years of survival.

Benign skeletal tumors (like osteoma, chondroma, bone cysts) are rare but carry an excellent prognosis. After complete surgical excision, recurrence is uncommon and animals generally have a normal life expectancy.