What is osteosarcoma?
Osteosarcoma is a malignant cancer of the bone. In dogs, it usually occurs in the large and giant breeds such as Great Danes, St. Bernards, Dobermans and Rottweilers, but any breed can be affected. Osteosarcoma typically affects middle aged to older dogs, however, young adult dogs are also susceptible. Osteosarcoma most commonly affects one of the bones of the limb such as the shoulder, carpus (wrist) and stifle (knee). Occassionally, osteosarcoma can originate in the bones of the skull, ribs or spine. The cause of the tumor is unknown.
How is it diagnosed?
Pets may experience persistent lameness and/or swelling of the affected leg. Radiographs of the bone will alert your veterinarian to the likelihood of osteosarcoma, however, other diseases such as bacterial or fungal infections of the bone, bone injuries and other types of tumors can mimic the appearance of osteosarcoma. Thus, a fine needle aspirate of the bone or a bone biopsy must be performed to definitively diagnose osteosarcoma.
Osteosarcoma has a high potential for metastasis, therefore, the following diagnostics are recommended:
- Radiographs of the lungs
- Abdominal ultrasound
- Scintigraphy (bone scan)
- Blood work
How is it treated?
Treatment of osteosarcoma usually involves both local treatment of the primary tumor affecting the bone and systemic chemotherapy to help delay or prevent the onset of metastasis.
- Surgical Amputation of the affected limb is often considered for treatment. This procedure removes the tumor, which would in turn alleviate the pain and source of potential fracture. For some dogs, where amputation is not an option, limbsparing may be considered.
- Surgical limbsparing involves removal of the cancerous bone and replacement with a bone graft, which is fixed to the remaining normal bone with a bone plate. The risks involved include infection of the bone or skin/tissue in the surrounding area, which may require antibiotics and/or surgery with hospitalization and possible tumor recurrence.
- Stereotactic radiation therapy consists of 1-3 doses of radiation administered to the exact location of the bone lesion. The major risk of this procedure is bone fracture at the sight of the bone lesion. If fracture occurs, then amputation of the affected leg could be pursued or possible surgical fracture repair.
- Fractionated palliative radiation may be used to decrease pain and improve function of the affected leg. It is usually administered in four treatments once a week. Radiation therapy offers pain relief for 60-70% of dogs, however, fracture is a risk with this treatment.
- Chemotherapy can be done in conjunction with any of the above treatment options. Chemotherapy would consist of treatments administered intravenously every three weeks. Side effects are usually mild and can include gastrointestinal upset and white blood cell suppression. More severe side effects are uncommon, but may require hospitalization.
- Zoledronate, a bisphosphonate drug, is given to help slow or prevent bone lysis, thereby strengthening bone. Bisophonates have been shown to provide pain relief in up to 50% of dogs. These drugs are usually used in combination with chemotherapy and/or radiation therapy, but may occasionally be used alone.
What is the prognosis?
Osteosarcoma is not a curable cancer, however it is treatable. Local disease control in combination with systemic chemotherapy can give your pet many months to years of good quality life.