Osteosarcoma in Dogs
What is Osteosarcoma?
Osteosarcoma is the most common bone cancer in dogs. It most often develops in the limbs of large-giant breed dogs. This tumor is locally aggressive (meaning it both destroys existing normal bone and makes abnormal new bone) and it also readily spreads to other places in the body (called metastasis).
Diagnostic tests are recommended to determine which sites in the body are involved. These tests include:
- Complete blood count (CBC)
- Serum biochemistry panel
- Urinalysis (U/A)
- Regional lymph node evaluation
- Thoracic radiographs
Treatment of osteosarcoma is aimed at both removing the painful tumor and using systemic medication to delay the onset of metastasis. Removal of the tumor requires amputation for the vast majority of affected dogs. While this is a big surgery, most dogs do very well following an initial adjustment period. Approximately two weeks following surgery, we recommend systemic chemotherapy in an effort to delay or prevent metastasis. Platinum (cisplatin or carboplatin) and doxorubicin have efficacy against this form of cancer. Treatments are given at 2-3 week intervals for a total of 4-6 treatments. Chemotherapy drugs work by targeting fast-growing cells and cancer cells divide faster and abnormally compared to normal cells. Because of this, chemotherapy preferentially destroys cancer and spares normal tissues. There is the potential for some normal tissues with rapid growth rates (intestinal lining, bone marrow, hair cells) to be transiently damaged by chemotherapy. However, our goal in treating cancer in animals is quality of life, so the dosages are lower than those used in people, and we do not normally see significant toxicity with chemotherapy.
There is always some risk when a drug is given for the first time, and the oncologist will discuss what types of side effects may develop and what you should watch for. If the pet has no problems the first time they receive a drug, they should have no problems with subsequent treatments of that drug. If the pet experiences any side effects, we address them as needed and lower the dosage of the causative drug for future treatments to prevent recurrent problems.
With surgery alone, most dogs experience a good quality of life for approximately 4-6 months. With the addition of chemotherapy, survival times extend to approximately 10-12 months.
Following completion of chemotherapy, or if chemotherapy is not pursued, metronomic therapy may be considered. Metronomic chemotherapy involves the administration of chronic oral low-dose chemotherapy (cyclophosphamide) in conjunction with other medications (carprofen or deramaxx and doxycycline). It is believed that this treatment approach may inhibit angiogenesis (new blood vessel growth) and thereby inhibit tumor growth.
If amputation is not an option, palliative radiation therapy can be considered. Palliative radiation therapy consists of two consecutive twice-daily doses of radiation therapy and is aimed at alleviating pain, inflammation, and swelling associated with the tumor. Approximately 70% of patients with osteosarcoma benefit from palliative radiation therapy with relief lasting 2-4 months. We recommend that the treatment be repeated in one month if no disease or symptom progression is noted in hopes of extending the duration of response.
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