Osteosarcoma in Dogs and Cats
Osteosarcoma is the most common form of bone tumor in dogs and cats. It’s more common in large breeds but can develop in any size dog. These tumors typically form on the long bones of the leg, but they can form on any bone in the body. Continue reading to learn more about this type of tumor, including diagnosis and treatment options.
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Osteosarcoma in Dogs vs Cats
Osteosarcomas are tumors of the bone. In dogs, they tend to be more common in larger and giant breeds and often develop around 6 to 8 years of age, although they’ve been reported in dogs as young as 18 months old. Any size dog can potentially develop this type of tumor and there is an increased risk in dogs that have metal plates present (often present after cranial cruciate ligament surgery or a fractured bone that was fixed) or after radiation therapy. In dogs, osteosarcomas are aggressive and tend to metastasize early, often before the main bone tumor is found.
Osteosarcomas in cats tend to be much less aggressive than in dogs. There is a link to vaccine-induced sarcomas that can involve the bone in some cats.
Common Symptoms of Bone Cancer in Dogs and Cats
Lameness is the most common symptom noted. The lameness can be mild initially and often resolves or improves greatly with pain medications like non-steroidal anti-inflammatories. Over time, the lameness and pain will increase and not be as responsive to pain medications anymore.
You may also notice a firm swelling along the affected leg and pain in the region. In dogs, these tumors tend to form closer to the shoulder and knee area.
Sometimes, the leg can break when your pet is just walking around or playing at home. These are called pathologic fractures and occur because the osteosarcoma eats away at the bone, making it weak in certain areas.
How are dogs tested for osteosarcoma?
Radiographs (x-rays) of the leg or affected area are a necessary step. On the radiographs, the bone tumor will look almost like a snow globe or spider web with swelling and patchy areas of bone present. Other diseases can cause a similar appearance like a deep fungal or bacterial infection, other types of cancer, metastasis, or even a bone cyst.
Once the radiographs are taken of the leg and there are changes suggestive of osteosarcoma, your vet will also obtain radiographs of the lungs to look for any signs of metastasis or spread of cancer. 90% of dogs will have microscopic metastasis by the time the main tumor is found - this means that you may not see it on an x-ray right away. About 7% of dogs will have metastasis that is visible on radiographs at the time of diagnosis.
A PET CT Scan, nuclear scan, and other advanced imaging may be recommended to look for the microscopic spread of cancer, but these types of tests are typically only available at universities and specialty hospitals.
What are the treatment options for bone cancer in pets?
After the imaging is completed, you and your vet may decide to proceed with a bone biopsy under general anesthesia or amputation of the affected limb. Once a biopsy has been taken or the entire limb is removed, the bone can be sent to the lab for further testing and confirmation of osteosarcoma or other disease.
Some specialty hospitals also offer a “limb-sparing” procedure where just the diseased bone is removed and a graft of another bone is inserted in its place. This type of surgery is often expensive, has a high risk of complications such as infection, fracture, etc. and the survival time is similar to dogs that had a limb amputation.
Most dogs and cats do very well after an amputation and can get around easily after the post-operative period.
Since most osteosarcomas have already spread by the time the main tumor is found, survival time with surgery alone is typically only 4 months. With additional treatment, the survival time can be extended greatly.
What additional treatments are available?
Chemotherapy after amputation can extend the life expectancy from 4 months to 10-12 months, with 20% of dogs surviving for over 2 years.
If surgery isn’t an option (cost, poor long-term prognosis, a tumor on a bone not possible to amputate), you can also consider radiation therapy to help shrink the tumor and provide pain control. This does require anesthesia for each treatment. Traditional radiation treatment and stereotactic radiation therapy are both options. With stereotactic, the radiation is given at a higher dose in a more limited area.
Pamidronate, a bisphosphonate, is an injectable drug given IV every 3 to 4 weeks. It can reduce pain, slow tumor growth, and help stabilize the bone.
Aggressive pain medication combinations can provide pain relief, but will not affect survival times.
There are studies currently underway for autologous vaccines for osteosarcoma, but none are commercially available yet. Contacting your local vet school hospital and other local specialists to see if they’re taking part in any of the studies may be worthwhile.
There are also studies underway on various medications that are injected into the tumor site to provide pain relief if surgery isn’t an option.
Finally, Palladia, a medication for mast cell tumor treatment, has also shown promising effects in dogs with metastatic osteosarcomas.
Final Note on Osteosarcoma in Cats
Luckily, in cats, these tumors rarely metastasize. This means amputation of the limb is often curative and your cat can go on to enjoy many more happy and comfortable years. It’s recommended to keep your cat indoors if they have an amputated limb since they won’t be able to get away from predators as well anymore.
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