Bone tumors in dogs:
Primary bone tumors in dogs are most commonly seen in large and giant breed dogs. The most common bone tumor is called osteosarcoma, which accounts for up to 85% of cases. Osteosarcomas arise from the bone cell, causing destruction of normal bone and proliferation of cancerous bone. Other less common tumor types that arise in the bone include fibrosarcoma (fibrous cells), chondrosarcoma (cartilage cells), synovial cell sarcoma (joint cells). The most common site of spread is the lungs, and uncommonly other bones and draining lymph nodes (<8% of cases). Most commonly, bone tumors arise near the wrists, shoulders, and knees. Additional diagnostic tests may be recommended based on your dog’s signs, bloodwork, and treatment decisions.
Palliative (pain control) treatment options:
- Pain medications to keep your pet comfortable. Osteosarcomas tend to cause discomfort or pain in most dogs due to inflammation, bone damage, or nerve pain. Pain management is very important for all dogs with bone tumors. Survival times are weeks to months depending on severity of signs.
- Amputation of the affected limb. Amputating the limb quickly and effectively removes the source of pain. Most dogs (even if they have concurrent arthritis) do very well with amputation. Median survival time is 4-5 months and patients typically succumb to nodules in the lungs. See tripawds.com for owner testimonials.
- Palliative radiation. Radiation is a type of local treatment in which high doses of x-rays are delivered to the tumor to decrease pain and inflammation. It is performed under a light plane of inhalant anesthesia so the patient remains still during the procedure. The anesthesia typically lasts 10-15 minutes, and animals wake up shortly thereafter. About 85% of patients have decreased pain, improved function, and increased quality of life for about 2- 3 months. If signs recur after 2-3 months, sometimes a second course of palliative radiation is elected.
Intermediate treatment option:
- Palliative radiation + chemotherapy. This involves palliative radiation (see above) plus four doses of carboplatin chemotherapy. The median survival time for dogs in this treatment group is 8 months.
Definitive treatment options:
- Amputation + chemotherapy. This is the gold standard treatment for dogs with osteosarcoma. Chemotherapy is started two weeks after the amputation. The median survival time is one year, and dogs usually succumb to nodules in the lungs.
- Stereotactic radiation therapy (SRT)+ chemotherapy. SRT is a more precise, high dose form of radiation therapy. A CT scan is required for radiation simulation and to make sure your pet is a good candidate for this treatment. The images are then imported into the radiation computer planning system, allowing for higher doses of radiation to be delivered into the tumor. In addition, this form of radiation also allows for better sparing of the normal surrounding soft tissue and skin. This treatment is given with zoledronate (see below) and four doses of carboplatin. Median survival time is up to a year, and dogs usually succumb to nodules in the lungs.
- Limb sparing surgery + chemotherapy This type of surgery is typically reserved for distal radius (wrist) tumors. The surgery removes the cancerous part of the bone, and bone plates and grafts are used to rebuild the limb. This procedure requires lifelong rechecks. There is a high chance of surgical site infection, which typically remains for the remainder of the dog’s life. Carboplatin chemotherapy is started two weeks after surgery or once the surgical site is well healed. Median survival time is about 1 year, and most dogs succumb to lung nodules.
Carboplatin chemotherapy:
Chemotherapy is surprisingly much better tolerated by dogs and cats versus people. Carboplatin chemotherapy is a drug that has been used for many years in human and veterinary oncology, and can be used for several different tumor types. It is administered as a bolus over a few minutes. Carboplatin is given once every three weeks for four total doses. The goal is to lower the risk and slow down the formation of lung nodules in patients with bone tumors. Without carboplatin, most dogs will die of lung spread within 4 – 5 months. If carboplatin is utilized, we can achieve a median survival time of 1 year in most patients. This chemotherapy is used in all “definitive treatments” and can be added to palliative radiation. Adverse side effects are possible in patients receiving any type of chemotherapy. Only about 30% of patients will have side effects, which are most commonly a day or two of decreased appetite or diarrhea. Since all chemotherapy patients are sent home with anti-nausea and anti-diarrhea medications, we expect that most side effects can be properly addressed at home by their owners. Less than 10% of patients need to return to the hospital from side effects, which are usually due to dehydration or infection secondary to immune suppression. There is a <1% chance of mortality.
Possible side effects include:
- Your dog may experience a low white blood cell count (neutropenia), which predisposes them to secondary infections. For this reasoning, we recommend getting bloodwork (CBC) at GCVS or your primary care veterinarian at one and two weeks’ time following the initial dose. If the white blood cell count is low enough, antibiotics will be prescribed to lower your dog’s risk of getting an infection.
- Stomach or intestinal upset can be seen in 30% of patients. The most common signs are nausea, decreased appetite, or diarrhea. Less commonly, dogs may also have anorexia or vomiting. Please call your veterinarian if 5 of 6 of these signs become moderate in nature or last more than 24 hours. Cerenia or metronidazole can be used to help at home.
- Rarely, kidney damage may occur. These cases are usually ones that had pre-existing kidney elevations on blood work prior to starting chemotherapy. We periodically assess kidney values on all carboplatin patients to monitor for this risk.
Hair loss is uncommon in veterinary patients undergoing chemotherapy treatment. However, we can see certain breeds have thinning hair or delayed regrowth time if an area is shaved. Hair thinning is usually in dogs that have continuously growing hair including poodles, maltese, etc.
Bisphosphonates (zoledronate, pamidronate)
This is a class of injectable drugs who act to inhibit the osteoclast (type of bone cell that resorbs bone), causing improved comfort and increased utilization of the leg in around 30% of patients. Side effects include kidney damage, therefore we monitor kidney values when getting these drugs. They can be administered once a month in patients who still have their limb (elected for radiation, limb sparing surgery, or pain management alone).
Other information:
It is important to remember that patients are at risk for pathologic fracture if the leg is not amputated. The risk of fracture is very patient dependent and it is impossible to predict when or if it may happen. If this occurs, your dog may show a sudden increase in pain. Fracture is considered a medical emergency.
Please let us know if you have any additional questions or concerns about your dog’s options.
