There are two broad types of bone cancer in dogs: primary and metastatic. Primary bone cancers start in the cells within the bone. Metastatic cancers start in different tissues or organs and move to the bone.
In dogs, primary bone cancers are by far the most common. The opposite is true in humans, where metastatic bone cancers are the more common type.
Specifically, osteosarcomas are the most frequent diagnosis for bone cancers in dogs. This is when the cells in a bone’s growth plates — regions of expansion — become cancerous. Around 85% of all bone cancers in dogs are osteosarcomas.
Other types of primary dog bone cancers are very rare and include:
- Chondrosarcoma. This is the second most common type of bone cancer in dogs. It primarily affects bones in the ribs and nasal cavities.
- Multiple myeloma. This is a bone marrow cancer that affects white blood cells.
- Fibrosarcoma. This cancer affects a cell type in bones called fibroblasts.
- Liposarcoma. This cancer affects fatty tissue stored in bones.
- Hemangiosarcoma. This cancer affects blood vessels — in this case, ones that are associated with bones.
Primary bone cancers can become metastatic and spread to the rest of your dog's body. Osteosarcomas do this frequently. In fact, in 80% of cases of osteosarcoma, the cancer also spreads to your dog's lungs. This spread is the main cause of death in most dogs with osteosarcoma.
There are at least 10,000 new cases of osteosarcoma in dogs each year. This is fifteen times more common than in humans.
What Causes Bone Cancer in Dogs?
Although the causes of bone cancer in dogs are not fully understood, researchers believe that there’s a strong genetic link. For example, 15% of all Scottish deerhounds — a breed of dog — develop osteosarcomas.
In general, large and giant breeds are the most likely to develop osteosarcomas. The mastiff terrier group — which includes boxers, golden retrievers, and mastiffs — develops osteosarcomas the most often.
Other potential contributing causes include:
- Gender. Males develop osteosarcomas 20% to 50% more often than females.
- Rapid growth. Bone cancer develops more often when your puppy’s bones get bigger at a very fast rate. Modern dog foods modify nutrient amounts to help slow down this process.
- Metallic implants for fractures. Cancers can occasionally develop in the same region that implants were previously used to repair a broken bone in your dog.
How is Bone Cancer in Dogs Diagnosed?
In order to diagnose bone cancer, your veterinarian will need to perform a full physical exam accompanied by blood tests, imaging, and a biopsy of the supposedly cancerous tissue.
The biopsy may only remove a small portion of the cancerous tissue for the sake of determining the type of cancer, or it may fully remove the entire tumor. This step is important because it helps your vet understand how advanced your dog’s cancer is and what the appropriate treatment should be.
What Are the Symptoms of Bone Cancer in Dogs?
The symptoms of your dog's bone cancer depend on where it develops. For osteosarcomas, the most frequent location is in one of your dog's limbs.
Osteosarcoma symptoms can include weakness, lameness, and pain in their limb. Osteosarcoma can also lead to a break in the bone at the spot where the tumor is located. Any broken bone in the limb of a large dog should be investigated as a possible case of osteosarcoma.
Axial osteosarcoma refers to a tumor located anywhere but the limbs, including the:
In these cases, the tumor forms a large, solid mass that can also be quite painful.
The pain from tumors in both locations can lead to other symptoms, including:
- Refusal to — or difficulty with — exercise
What Is the Treatment for Bone Cancer in Dogs?
There’s no cure for bone cancers in dogs, but they can be treated. The main treatment for bone cancers — and osteosarcoma in particular — is to remove the tumor or cancerous region.
In most cases, this involves complete removal of the affected limb. Dogs are usually able to recover from this surgery quickly and to resume all former activities. In fact, the removal is often more difficult for the owner than the pet.
Physical therapy can help your dog adjust after one of their limbs is removed.
For axial osteosarcoma, a different type of surgery may be needed to extract the tumor. After surgery, even if just a few cancerous cells are left behind, there’s a good chance that the tumor will grow back.
Regardless of the location of the tumor, your veterinarian will recommend chemotherapy treatment after the surgery. This is done to prevent any remaining cancer from spreading, or metastasizing. Chemotherapy can increase your dog's lifespan more than just amputation or removal.
Radiation therapy is also available if you don’t want to amputate and only want to provide palliative — or end of life — care. This treatment can help to shrink the tumor and reduce pain. It shouldn’t be used if the bone is too weak and likely to break when the tumor is treated.
What Is the Life Expectancy of a Dog with Bone Cancer?
Since bone cancers are not curable, your dog will have a limited lifespan following this diagnosis. Around 50% of diagnosed dogs will survive for a year if treated.
For osteosarcomas, estimates depend on where the tumor is located. If the tumor is in the mandible or scapula — the jaw or shoulder blade — average survival is around 18 months. If it’s in a limb, the average survival is 11 months. If it’s in the spine or skull, survival is estimated at 6 months, and only at 2 months if it has already spread outside of the skeletal system.
It’s important to see your veterinarian as soon as you notice any symptoms, like limping, or feel any hard masses in your large or giant dog breed. The sooner you seek treatment, the more likely your dog is to respond.