Canine and Feline Osteosarcoma

Osteosarcoma (OSA) is the most common primary bone tumor in dogs and, although less frequent, it is also reported in cats. This malignant neoplasm is highly aggressive, locally invasive, and characterized by an almost inevitable metastatic potential, most commonly to the lungs. In dogs, OSA predominantly affects large and giant breeds and tends to arise in the metaphyseal regions of long bones, particularly the distal radius, proximal humerus, distal femur, and proximal tibia. Cats are less commonly affected, but their disease course is often slower and metastasis occurs less frequently than in dogs. Clinical signs typically include progressive lameness, pain, swelling, and, in advanced cases, pathologic fractures. Accurate diagnosis and staging are essential, as treatment strategies and prognosis depend heavily on tumor location, presence of metastasis, and systemic involvement.

Canine and Feline Osteosarcoma NAVLE Review

Overview

Osteosarcoma (OSA) is the most common primary bone malignancy in dogs and also occurs (much less frequently) in cats. It is highly aggressive, locally destructive, and almost always metastatic. Clinicians preparing for exams should focus on its epidemiology, signalment, diagnostic features, treatment options, and prognostic factors.

Key Facts & Signalment

Species & Breeds: Large/giant breed dogs affected most often (Great Danes, Rottweilers, Greyhounds, etc.). Cats have lower incidence and less aggressive behavior.
Age: Typically middle-aged to older dogs, though some young dogs are affected.
Anatomic Location: Appendicular skeleton predominates (distal radius, proximal humerus, distal femur, proximal tibia). Axial OSA (mandible, skull, spine, ribs) has worse prognosis.

Pathophysiology and Behavior

Primary bone tumor producing malignant osteoid; histologic subtypes include osteoblastic, chondroblastic, fibroblastic, and mixed.
Early microscopic metastases are nearly universal; lungs are the most frequent site; metastases often present at diagnosis or develop quickly.
Local invasion leads to cortical destruction, periosteal reaction, soft tissue swelling, pain, and risk of pathological fractures.

Clinical Signs

Progressive lameness or acute onset lameness without trauma
Local swelling over growth areas of long bones
Pain on palpation or manipulation, heat, possibly pathologic fracture
Systemic signs typically from metastasis are less common at onset but important later (respiratory difficulty if lung nodules)

Diagnostics

Radiographs: Mixed lysis and proliferation (“sunburst” pattern), cortical destruction, Codman’s triangle, soft tissue swelling. Thoracic radiographs always to check for lung metastasis.
Biopsy: Definitive diagnosis requires bone biopsy (open, trephine, or Jamshidi needle) to confirm tumor osteoid and subtype.
Staging: Blood chemistry (incl. ALP), CBC, thoracic imaging, sometimes advanced imaging for axial tumors. Elevated ALP is a negative prognostic indicator.

Treatment

Curative-intent: Amputation of affected limb (or appropriate radical resection in axial cases) followed by adjuvant chemotherapy (common agents: carboplatin, cisplatin, doxorubicin) to extend survival.
Limb-sparing surgery: Possible in select cases to preserve limb; risk of complications higher, needs good case selection.
Palliative care: When curative treatment is not feasible: pain control (NSAIDs, opioids), radiation therapy for local pain relief, bisphosphonates to slow bone destruction.

Prognosis & Survival

Without treatment: survival is usually only a few months.
With amputation + chemotherapy: median survival in dogs approx 9-12 months, though individual variation is considerable; younger age, lower ALP, smaller tumor, good surgical margins improve prognosis.
In cats: survival after amputation alone may exceed a year; metastasis less common than in dogs.

High-Yield Points for Exam

Always check lungs via thoracic radiographs when diagnosing OSA.
ALP elevation is a negative prognostic indicator.
Amputation + chemo extends survival significantly over surgery alone.
Axial locations (mandible, skull, ribs, pelvis) harder to treat, worse prognosis.
Cytologic suspicion via FNA supports diagnosis, but biopsy is required for definitive diagnosis.

Conclusion

Canine osteosarcoma is a rapidly progressive, highly metastatic primary bone tumor most often affecting large breed dogs. Accurate diagnosis via radiography and biopsy, staging, and aggressive local plus systemic therapy are essential. Prognosis remains guarded but can be meaningfully extended with the standard of care. Cats fare somewhat better but remain a minority of cases. Veterinary professionals should be prepared to recognize this disease and understand the strategies for management.