What is osteosarcoma?
Osteosarcoma is an aggressive type of bone cancer. It usually develops in the long bones of the legs, but can occur in other bones as well, such as the skull, pelvis, ribs, and vertebrae.
This cancer starts when the cells that normally create and break down bone begin to grow abnormally, forming a tumor. Osteosarcoma can also affect non-bony tissues, including the mammary glands, spleen, liver, and kidneys. When it occurs in these tissues, it is called extra-skeletal osteosarcoma.
What causes this type of tumor?
The reason why a particular pet may develop this, or any tumor, is not straightforward. Very few tumors and cancers have a single known cause. Most seem to be caused by a complex mix of risk factors, some environmental and some genetic or hereditary.
Osteosarcomas appear to affect large-breed dogs more commonly than small breeds. Reported predisposed breeds include boxers, Doberman pinschers, golden retrievers, German shepherds, Scottish deerhounds, Leonbergers, Great Danes, greyhounds, Irish setters, Irish wolfhounds, and rottweilers.
What are the signs of osteosarcoma?
Osteosarcoma is very painful. If your dog has an osteosarcoma of the limb (called appendicular osteosarcoma), you may notice the following signs:
- Distinct swelling, lameness (limping)
- Lethargy (reduced energy, tiredness)
- Loss of appetite
- Reluctance to walk or play (due to pain caused by the tumor on the bone)
The most common areas for osteosarcomas in dogs are the long bones of the legs, the front knee or wrist (radius/ulna above the carpus), and the bones below the knee (tibia/fibula). Osteosarcoma can also develop in other bones, including the toes, skull, pelvis, ribs, and vertebrae.
Dogs with osteosarcoma of the jaw have symptoms that include:
- Swelling of the jaw
- Difficulty opening the mouth
- Excessive salivation
- Reluctance to eat (due to pain)
If an osteosarcoma develops elsewhere in the skull or vertebrae, you may observe swelling and pain in the head or along the back.
How is osteosarcoma diagnosed?
Your veterinarian will notice signs during a physical examination. Most dogs with osteosarcoma will limp on the affected limb. Swelling is usually noted where the tumor has grown, and the area will be warm to the touch due to a tremendous amount of inflammation. The area is often very painful.
Your veterinarian will take X-rays of the region. On X-rays, osteosarcomas appear lytic (meaning pieces of bone are missing) or “moth-eaten,” due to the loss of normal bone tissue. Fractures can be present if the bone has weakened.
Once a lesion is suspected, a more definitive diagnosis may be obtained by a fine needle aspiration (FNA). This procedure involves sedating your dog and then using a small needle with a syringe to suction some cells directly from the lesion. A veterinary pathologist then examines the slide under a microscope. If this procedure does not provide a diagnosis, a bone biopsy may be required. In most cases, lytic bone lesions found on X-rays indicate infection or cancer and further diagnostics are always recommended.
How does this cancer typically progress?
Osteosarcoma in dogs is extremely aggressive. About 90% to 95% of dogs will have micrometastasis at the time of diagnosis, meaning the cancer cells have already spread elsewhere, even though they are not detectable. For that reason, staging (searching for spread to other locations in the body) is always recommended in dogs with osteosarcoma.
Staging may include bloodwork, urinalysis, X-rays of the lungs, and possibly an abdominal ultrasound, CT, or MRI. If any lymph nodes are enlarged or feel abnormal, further sampling may be required.
How is osteosarcoma treated?
Without evidence of spread, the primary goal of treatment is local tumor control, which typically involves amputating the affected limb. Although the idea of amputation is unsettling for many dog owners, most dogs do very well after the surgery. As long as it is a safe and viable option as it provides significant relief from pain, surgery is almost always pursued.
Chemotherapy is nearly always pursued post-surgery to help control the disease for as long as possible. Other treatment options may also be available, including certain forms of radiation therapy. Chemotherapy has fewer side effects in dogs than in humans, and quality of life is maintained or improved. You may need a referral to a specialty veterinary center for these treatment options.
Is there anything else I should know?
Adequate pain control is of utmost importance. Discuss appropriate pre- and post-operative therapy and pain management plans with your veterinarian.
