Canine Osteosarcoma
Osteosarcoma (OSA) is the most common primary bone tumor in dogs. Its most common form affects the appendicular skeleton of large or giant breed dogs; however, it can also affect the axial skeleton as well, which occurs more frequently in smaller dogs. In dogs, it is a locally and metastatically aggressive disease that is very similar to the disease’s human form. This PowerPage will focus on the more common appendicular form with a brief review of the axial skeleton form of the disease.
Key Points
- Most commonly occurs in large and giant breed dogs in the metaphyseal regions of the appendicular skeleton
- Distal radius, proximal humerus, distal femur, proximal tibia (“away from the elbows and toward the knees”)
- Can present for chronic progressive lameness or acute lameness after an inciting incident such as jumping off the couch or out of the car
- Amputation of an affected limb is the most effective way to eliminate pain but is considered palliative as 90% of dogs will eventually develop metastasis
- Metastasis most commonly spreads to the lungs but can occasionally occur in lymph nodes or other bones
- Chemotherapy can help extend median survivals to 10-12 months
Diagnostics
Limb radiographs
- Classically a lytic and productive lesion at the metaphysis of the bone
- A diaphyseal lesion should raise red flags for the lesion potentially being metastatic from a primary tumor from somewhere else in the body
- Do not cross joints into adjacent bones
Figure 1. Lateral radiograph of a productive and lytic osteosarcoma lesion of the distal radius.
Image courtesy of DVM Insight.
Fine needle aspirate cytology
- Aspirate the center of the lesion
- Aspirates of the periphery often result in “reactive bone”
- Use ultrasound guidance to help insert the needle into cracks of the cortex
- Warn the owner about the possibility of pathologic fracture with aspiration or biopsy
Biopsy
- May be required for a definitive diagnosis in equivocal cases
Thoracic radiographs
- Pulmonary metastasis visible in less than 10% of cases at the time of diagnosis but will develop in the future in most cases
- Visible pulmonary metastasis portends a poor prognosis and therefore must be performed prior to treatment
Bone scan or nuclear scintigraphy
- Used to find or rule out suspected bone metastasis
- Technetium-99–hydroxymethylene diphosphonate binds to areas of active bone and is detected in imaging
- Sensitive, but poorly specific
- Increased uptake can occur with bone tumors, arthritis, fractures, or osteomyelitis
- Alternatively, full body radiographs can be performed
Bloodwork
- Elevation in alkaline phosphatase on a chemistry panel is associated with a worse prognosis
Treatment
Surgery
- Amputation is the most effective way to alleviate pain of bone destruction
- Palliative as most dogs will develop metastasis in the future
- Limb-sparing procedures
- Surgical removal of the bone tumor with replacement of a prosthetic at the ostectomy site
- Also considered palliative
- High rates of complications: chronic resistant infections, tumor recurrence, failure of surgical constructs
- Expensive and limited to experienced surgeons
Radiation therapy
- Can be effective in palliating the pain of bone tumors in up to 75% of cases, for about 2-3 months
- No detectable improvement in pain in 25%
- Pathologic fractures may be more likely to occur if pain is well controlled and use of the limb is increased
Chemotherapy
- Proven to extend survivals over surgery alone
- Chemotherapy protocols mostly consist of a platinum drug (cisplatin or carboplatin) as a single agent or in conjunction with Adriamycin (doxorubicin)
- Generally thought not to be effective if macroscopic disease is present
- Bisphosphonates (pamidronate) are osteoclast inhibitors that can help palliate pain in patients where surgery is not an option
Prognosis
Median survival times
- Amputation alone: 4-6 months
- Surgery (amputation or limb spare) with chemotherapy: 10-12 months
- Presence of macroscopic metastatic disease: 1-3 months
Axial osteosarcoma
- Make up 25% of all OSAs and occur more commonly in small- or medium-sized dogs compared to appendicular OSA
- Common locations: mandible, maxilla, scapula, ribs, spine, pelvis
- The mandible has a better prognosis compared to all other sites
- 70% 1-year survival with surgery alone
- Other locations generally thought to have aggressive clinical courses similar to the appendicular disease
