Thanks to advances in veterinary care, our dogs are living longer and enjoying life well into their golden years. However, a longer lifespan makes dogs more susceptible to old age-related health conditions, like cancer.

According to the American Veterinary Medical Association, about 25 percent of dogs will develop cancer.

Many types of cancer affect dogs. These cancers differ in several ways, including aggressiveness, location, symptoms, and prognosis.

Bone cancer in dogs is a common canine cancer. It is aggressive and progresses quickly, so early detection and treatment are crucial to providing a dog with bone cancer an ideal quality of life.

What is Bone Cancer?

Cancer is the uncontrolled growth of abnormal cells. Bone cancer is the uncontrolled growth of bone cells responsible for building bone (osteoblasts) and breaking down bone (osteoclasts). In healthy bone, osteoclast and osteoblast activity is tightly regulated. With bone cancer, this tight regulation is lost.

Bone cancer is malignant and very painful. Like other malignant cancers, bone cancer invades nearby tissues and metastasizes (spreads) throughout the body, frequently to the lungs. Bone cancer is unlike benign tumors, which do not invade other tissue or metastasize.

Bone cancer typically affects middle-aged- to older dogs.

Osteosarcoma represents 85 to 95 percent of canine bone cancers. It can affect all breeds, but large and giant breed dogs, such as Rottweilers and Great Danes, are most susceptible.

Osteosarcoma is classified as appendicular (limbs) or axial (skull, ribs, vertebrae, jaw bones). Appendicular osteosarcoma is more common in large and giant breed dogs, while axial osteosarcoma primarily affects small breed dogs.

Causes of Bone Cancer in Dogs

The exact cause of canine bone cancer is unknown. However, genetics play a prominent role in bone cancer development. Breeds that are genetically predisposed to osteosarcoma, for example, include large and giant breed dogs.  

Prior bone trauma caused by fracture, infection, or radiation therapy can also lead to bone cancer.

Other potential contributing factors include rapid growth and gender. Osteosarcoma tends to affect male dogs more than female dogs.

Symptoms of Bone Cancer in Dogs

The signs of bone cancer in dogs can be nonspecific. Also, these signs can depend on the primary cancer’s location. For example, primary bone cancer will have bone-related signs, while a secondary bone cancer will have symptoms related to its original location.

Here are examples of nonspecific signs of bone cancer in dogs:

• Irritability
• Weight loss
• Reduced appetite
• Difficulty sleeping
• Increased vocalization
• Increased heart rate

Bone-related symptoms of bone cancer are listed below:

• Limping
• Lameness
• Limb swelling
• Reluctance to exercise or play

If you notice any of these signs, take your dog to your veterinarian for further examination.

Types of Bone Cancer in Dogs

Bone cancer is either primary (originating in the bone) or secondary (originating elsewhere and spreading to the bone). Osteosarcoma is a primary bone cancer. 

Secondary bone cancers include:

• Chondrosarcoma (cancer of the cartilage)
• Fibrosarcoma (cancer of the fibrous tissue)
• Hemangiosarcoma (cancer of the blood vessels)

Stages and Progression of Bone Cancer in Dogs

Staging in bone cancer helps determine the type of bone cancer and the extent of its spread and provides general health information. A veterinarian uses cancer staging to develop an appropriate treatment plan and determine a prognosis.

Bone cancer staging in dogs follows general cancer staging:

• Stage I: Low-grade tumor with no metastasis
• Stage II: High-grade tumor without metastasis
• Stage III: High-grade tumor with metastasis

Although early detection is always recommended, osteosarcoma is so aggressive that even early detection does not guarantee an improved treatment and survival outcome.

Diagnosing Canine Bone Cancer

Diagnosing bone cancer in dogs involves a history and physical exam, followed by laboratory and imaging tests. For the history, your veterinarian will ask detailed questions about which symptoms your dog has and when those symptoms first appeared.

The physical exam will include an orthopedic exam, which will focus on your dog’s bones and joints. Your vet will pay close attention to areas of pain and swelling.

Laboratory testing, such as bloodwork and biopsy, will provide more information about your dog’s general health and specific information about the bone cancer. Bloodwork provides information about organ function. For example, elevated liver enzymes indicate decreased liver function.

A biopsy is used to definitively diagnose bone cancer. Your veterinarian will sedate your dog to obtain a cancer tissue sample and have the sample analyzed by a veterinary pathologist.

Imaging tests for bone cancer include X-rays, abdominal ultrasounds, and advanced imaging.

X-rays are performed of the affected limb. Examples of X-ray findings that suggest bone cancer are listed below:

• “Moth-eaten” appearance, indicating bony destruction
• “Sunburst” appearance, showing abnormal bone changes
• Pathological fractures (fractures not caused by trauma)
• Soft tissue swelling around the affected bone

X-rays are also taken of the chest to look for lung metastasis. Abdominal ultrasounds can demonstrate abdominal metastasis.

Advanced imaging – computed tomography and magnetic resonance imaging (MRI) – provide detailed images of the extent of nearby tissue invasion and distant metastasis.

Bone Cancer Treatment Options for Dogs

The treatment goals for bone cancer are to treat the cancer locally and prevent metastasis. Unfortunately, achieving long-term control is difficult because bone cancer in dogs can be so aggressive.

Several treatment options are available for bone cancer treatment.

Amputation

For appendicular osteosarcoma (affecting the limbs), entire limb amputation is the recommended treatment option. Complete limb amputation not only removes the entire tumor but also provides relief from tumor-related pain.

With axial osteosarcoma, however, surgery may not completely remove the tumor. In these cases, additional treatment would be needed for local tumor control.

Chemotherapy

Chemotherapy is given after amputation to control cancer spread and, ideally, extend survival time. Most dogs tolerate chemotherapy well, experiencing mild side effects (e.g., reduced appetite) that last only a few days. Common chemotherapy drugs for osteosarcoma are doxorubicin and carboplatin.

Radiation Therapy

Radiation therapy is a treatment option if amputation is not possible or practical. It can be a palliative treatment to relieve discomfort without providing a cure.

Pain Medication

Pain control is an integral aspect of bone cancer treatment. Pain medication can help improve quality of life while receiving other cancer treatments. Types of pain medication include opioids and non-steroidal anti-inflammatory drugs.

The Cost to Treat Bone Cancer in Dogs

Bone cancer treatment in dogs can easily cost thousands of dollars. Each type of treatment option will have its own set of expenses. We’ve listed examples of some of the expenses below.

• Amputation: pre-surgical bloodwork, anesthesia, pre- and post-pain medication, post-surgical in-hospital monitoring
• Chemotherapy: cost of medication, administration of the chemotherapy (if given intravenously)
• Radiation therapy: anesthesia, type of radiation therapy performed, number of radiation therapy treatment sessions
• Pain medication: cost of medication

In addition to these costs, there will also be the cost of follow-up visits to take X-rays and perform laboratory testing. Follow-up visits are typically every 2-3 months.

Pet insurance can help defray the high cost of bone cancer treatment. However, pet insurance may not cover pre-existing conditions, so it is best to have an insurance policy in place before the diagnosis.

Prognosis for Bone Cancer in Dogs

Dogs with bone cancer often have a poor prognosis. Even with early detection and treatment, including amputation and chemotherapy, life expectancy is only about one year after diagnosis.

Without treatment, the life expectancy is significantly shorter – about four months.

Because osteosarcoma is so aggressive, it is nearly impossible to prevent metastasis. Most dogs with bone cancer will eventually succumb to lung metastasis.

How to Prevent Bone Cancer in Dogs

It is not possible to prevent bone cancer. If your dog is genetically predisposed to bone cancer, monitor your dog for signs of bone cancer and seek veterinary treatment early.