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 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 or cancer, is not straightforward. Very few 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.
What are the signs of osteosarcoma?
Osteosarcoma is very painful. If your cat has an osteosarcoma of the limb (called appendicular osteosarcoma), you may notice the following signs:
- Lameness (limping)
- Distinct swelling
- Lethargy (reduced energy, tiredness)
- Loss of appetite
- Reluctance to walk or play (due to pain caused by the tumor on the bone)
In cats, osteosarcomas occur most commonly in the hindlimbs (femur and tibia). They can also develop in the skull (most commonly in the oral cavity), pelvis, ribs, and vertebrae. Cats with osteosarcoma of the jaw have symptoms that include:
- Swelling of the jaw or difficulty opening the mouth
- Excessive salivation
- Reluctance to eat (due to pain)
How is osteosarcoma diagnosed?
Your veterinarian will notice signs during a physical examination. Most cats 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 enough.
Once a lesion is suspected, a more definitive diagnosis may be obtained by a fine needle aspiration (FNA). This procedure involves sedating your cat 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 cats is less aggressive than in dogs, and metastasis (spread to other areas of the body) is much less common than in dogs. Even so, staging (searching for potential spread to other locations in the body) is recommended. Staging may include bloodwork, urinalysis, X-rays of the lungs, and possibly an abdominal ultrasound. 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 cat owners, most cats 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 not typically pursued in cats, because the disease is usually controlled by amputation. Radiation therapy is sometimes undertaken if the tumor cannot easily be surgically removed.
Is there anything else I should know?
Adequate pain control is of the utmost importance. Discuss appropriate pre- and post-operative therapy and pain management plans with your veterinarian.