A Pet Parent’s Guide to Osteosarcoma (Bone Cancer)

A persistent limp or a sudden, painful swelling on your pet’s leg can be alarming. One of the most serious causes for these signs is osteosarcoma, the most common type of bone cancer in dogs and cats. A diagnosis of osteosarcoma is incredibly difficult to hear, and at Harmony Pet Clinic, we are here to provide you with the clear, compassionate guidance you need to navigate this challenging journey.

What is Osteosarcoma?

Osteosarcoma is an aggressive cancer that arises from the cells that form bone. It is a destructive tumor that weakens the bone, causing significant pain and putting the bone at risk of fracturing from even minor trauma (this is called a pathologic fracture). While it can develop in any bone, it most commonly appears in the limbs, typically “away from the elbow and near the knee.”

Osteosarcoma in Dogs

Osteosarcoma is much more common in dogs than in cats, and it has a strong predisposition for large and giant breeds like Great Danes, Rottweilers, Irish Wolfhounds, and Golden Retrievers. It is a highly aggressive cancer in dogs, with a very high rate of early, microscopic spread (metastasis) to other parts of the body, most often the lungs.

Signs & Treatment in Dogs

• Limping: This is often the first sign. The lameness may start subtly and then become persistent and more severe.
• Swelling: A firm, painful swelling may develop on the affected leg or bone.
• Pain: Your dog may cry out when the area is touched, be reluctant to play, or show changes in behavior due to discomfort.
• Diagnosis: The first step is an x-ray of the affected area, which often shows a characteristic “sunburst” or “moth-eaten” appearance of the bone. A definitive diagnosis requires a bone biopsy.
• Treatment: Because this cancer is so painful, treatment focuses on two goals: alleviating pain and slowing the spread. The gold standard for pain relief is amputation of the affected limb. While this sounds drastic, dogs adapt incredibly well on three legs and are almost immediately relieved of the constant, severe pain. To fight the cancer that has almost certainly already spread, chemotherapy is started after the surgery.

Osteosarcoma in Cats

Fortunately, osteosarcoma is much less common in cats. When it does occur, it tends to be less aggressive than the canine form. The signs are similar—limping and swelling—but the rate of metastasis is significantly lower. Because of this, treatment can often be more successful. For many cats with osteosarcoma in a limb, amputation alone can be curative, and follow-up chemotherapy is not always necessary.