Overview

Osteosarcoma (OSA) is one of the most common types of bone cancer in dogs, often diagnosed in large or giant breed dogs, such as Rottweilers, Great Danes, St. Bernards, and Golden Retrievers. The tumor commonly grows on the long bones of the forelimbs or hindlimbs, causing pain and lameness. Unfortunately, this is a very aggressive tumor and often metastasizes (spreads to the lungs) early in the disease. While there is no cure for OSA, there are treatment options to help delay the progression of the disease and alleviate pain. 

Cause

OSA is a malignant bone cancer formed from abnormal production of specific cells in bones that are intended to create and break down bone. As the tumor grows, it destroys normal bone and replaces it with cancerous bone, making the bone susceptible to breaking (pathologic fractures). The exact cause is unknown, but there is likely a genetic component, given the predisposition for certain breeds, particularly large-breed dogs. OSA is more common in older dogs around seven years of age, but a small subset of dogs may also develop OSA as young adolescents.

While OSA commonly affects the forelimb or hindlimbs (appendicular OSA), less commonly, it can also occur on bones such as the jaw, rib, or pelvis (axial OSA). Axial OSA is less specific to large breed dogs and may be seen in smaller breeds. While less common, OSA has developed at the site of a previously healed fracture or chronic osteomyelitis (bone infection), in association with metallic implants, or after exposure to radiation therapy. Rarely, OSA can occur outside of the bone (extraskeletal OSA) and affect tissues like the mammary gland or other internal organs. 

Clinical signs

OSA is often very painful. The most common signs of OSA may depend on the tumor location, often include:

• Lameness, or reluctance to walk
• Firm, localized swelling, most commonly on the limbs
• Loss of muscle mass to the affected limb

There may be less common or nonspecific signs secondary to pain such as loss of appetite or behavior changes.

Diagnosis

A combination of history, physical exam findings, and X-rays (radiographs) of the affected limb or swelling are used to diagnose OSA. Radiographs of the tumor often show a characteristic appearance consistent with OSA. In some cases, a fine needle aspirate (FNA) or biopsy, which involves taking a sample from the tumor, may be recommended. A biopsy of the tumor is the only way to diagnose OSA definitively.

Additional testing to determine your dog’s overall health may be recommended, such as blood work, urinalysis, and chest radiographs to look for signs of metastasis (spread of disease).

Treatment

Osteosarcoma treatment may depend on several factors, including tumor location and individual needs, but the main focus is pain management and your dog’s quality of life.  You may be referred to a veterinary oncology specialist.

Unfortunately, there is no cure for osteosarcoma, but the best chance of extending time and quality of life includes multimodality therapy that involves:

• Pain management: Oral medications such as NSAIDs (non-steroidal anti-inflammatories), gabapentin, amantadine, opioids, or a combination are often used to control pain.
• Surgery: When OSA affects a limb, surgery to remove the limb (amputation) is often recommended as the best way to remove the tumor, manage pain from the tumor, and remove the risk of pathological fractures. If OSA occurs in a location other than the limbs, such as a rib or jawbone, local surgical resection is often recommended (e.g., removal of a rib or part of the jaw).
• Chemotherapy: Chemotherapy after amputation aims to delay the onset of metastasis and is often well-tolerated by dogs. Medications such as carboplatin given IV (intravenous) are often performed every three weeks for 4-5 months.

If surgery is not an option, pain management becomes the focus of care. Additional options for pain management besides the aforementioned oral medications when surgery is not pursued include Palliative Radiation Therapy (PRT) or IV bisphosphonate therapy, often performed by a specialist.

Limb-sparing surgery and stereotactic radiation therapy are additional alternatives to surgery. They are available through specialists, although not all dogs will be candidates for these types of treatments.

Outcome

OSA often carries a poor prognosis as it tends to behave aggressively, and unfortunately, there is no cure. Often, at the time of diagnosis, the tumor has already spread to the lung, whether those lesions are visible on radiographs or not (micrometastasis).

When surgery is combined with chemotherapy, the median survival time is about nine months, but individual dogs will vary in their response to treatment. Rechecks every 2-3 months may be recommended to monitor radiographs for metastasis. Unfortunately, even with multimodality therapy, metastasis to the lungs often occurs. 

Amputation without chemotherapy only serves as a form of pain management and fracture prevention but does not prevent the spread of cancer. Many dogs adjust quite well to three limbs and are much more comfortable after surgery, often returning to normal activities. The median survival time with amputation alone is four months.

Updated Aug. 2024