Osteosarcoma in Dogs: What You Need to Know
No pet parent wants to imagine the big C happening to their dog. Cancer is scary no matter the type, but bone cancer is extremely painful and serious. There's no such thing as a "good" type of cancer, but osteosarcoma is definitely one of the more aggressive ones.
Osteosarcoma in dogs is not very common, but when it does strike, it requires swift veterinary attention. Here's what pet parents need to know.
What Is Osteosarcoma?
Osteosarcoma is a malignant and aggressive tumor that affects the skeletal system of dogs, humans, and other animals. It often develops in the long bones of the limbs—especially the humerus, radius, femur, and tibia—but it can affect any bone in the body, including the jaw, skull, spine, pelvis, or ribcage. Osteosarcoma can grow rapidly, causing destruction of the bone that leads to severe pain, instability, and fractures.
There is also extraskeletal osteosarcoma, a rare form of this tumor that affects soft tissue sites such as the mammary glands, liver, kidneys, or spleen.
Osteosarcoma is the most common form of bone tumor seen in dogs. Rarer bone tumors include chondrosarcoma, fibrosarcoma, and hemangiosarcoma. Overall, bone cancer is fairly uncommon in dogs and even less common in humans.
What Causes Osteosarcoma?
Scientists are not sure exactly why osteosarcoma develops (or many other types of cancer, for that matter), but there does appear to be a genetic component. While this type of cancer can affect dogs of all breeds, it's most common in large and giant dog breeds, including:
Osteosarcoma occurs most often in middle-aged and senior dogs, but even young dogs can be affected.
What Are the Signs of Osteosarcoma in Dogs?
Bone cancer hurts! The first sign of osteosarcoma in dogs is often sudden pain in the affected area. If in a limb, the dog will likely begin limping and may hold up the painful leg. This limping may come and go at first, leading pet parents to believe it's just a minor issue like a sprain or strain. However, the limping will not go away with rest and medications, as it would with a minor injury.
As the tumor grows, you may notice swelling in the affected area. Over time, the pain becomes worse and the bone may actually break. Because of the bone destruction caused by cancer cells, these fractures will not heal with treatment.
How Fast Does Osteosarcoma Spread?
Osteosarcoma in dogs tends to metastasize quickly to other parts of the body, especially the lungs. The rate of this spread can vary from case to case, but many dogs already have metastasis by the time they show signs of pain. Early detection and treatment of osteosarcoma can prevent or slow the spread of this cancer.
Your veterinarian will do diagnostic tests to determine if the cancer has spread and how much. This is called staging and usually involves lab work, X-rays, and ultrasounds. Some dogs will need advanced diagnostic tests like CT or MRI. Your primary vet may refer you to a veterinary oncologist for staging and treatment.
How Is Osteosarcoma in Dogs Treated?
Because of the aggressive nature of this cancer and the severe pain it causes, treatment should be started ASAP. Specific treatment is dependent on the location of the tumor, but the primary goals of treatment are to alleviate pain and prevent or slow metastasis. Most dogs are treated with pain medications such as carprofen and gabapentin. Your veterinarian will discuss the best treatment options for your individual dog.
In most cases, the recommendation is to remove the primary tumor, if possible. This often involves amputation if the tumor is in a limb.
Most dogs adapt well to life as a tripod! Three healthy limbs are more than enough for dogs to run, jump, play, and enjoy life. Amputation removes the source of pain (recovery pain from surgery is much milder) and improves overall quality of life. Surgery may even cure the cancer or lead to remission if the cancer has not spread.
But surgery and amputation aren't synonymous; dogs with severe arthritis or other mobility issues are usually not good candidates for amputation. Depending on the tumor site, limb-sparing surgery may be an option. During this procedure, the vet will surgically remove as much of the tumor as possible. These dogs usually need chemotherapy as a follow-up treatment.
Some tumors cannot be removed with surgery due to their location. Fortunately, there are other treatment options available.
Chemotherapy is usually recommended as a treatment for metastasized cancer and after limb-sparing surgery. This typically involves a weekly trip to an oncologist over six months (or longer). Side effects of chemotherapy vary, but are often relatively mild in dogs compared to people. And while chemotherapy won't cure osteosarcoma, it can improve quality of life and may extend life expectancy.
Radiation treatments may be recommended as a palliative therapy for inoperable osteosarcoma. Here, dogs receive doses of radiation directed at the tumor in order to reduce pain. Radiotherapy will not cure osteosarcoma or extend life expectancy, but it can temporarily improve quality of life.
How Long Can Dogs Live With Osteosarcoma?
The life expectancy for dogs with osteosarcoma really depends on how much the cancer has spread. Sadly, without treatment, most dogs will succumb to this cancer within a few months. Treatment may extend life by a year or more. One study indicated that dogs with osteosarcoma who lived for more than a year after diagnosis had a median additional survival time of approximately eight months.
Each case is different, and your vet can help guide you through treatment and home care for your dog. The final stages of osteosarcoma can cause significant illness in dogs when the lungs are affected by metastasis, causing respiratory distress and pain. Euthanasia is often the most humane option when dogs are having more bad days than good.