Osteosarcoma in Pets: How to Recognize and Navigate This Aggressive Bone Cancer

This article has been reviewed and approved by Dr. Jaclyn Coble, Doctor of Veterinary Medicine and President of Sea Legs Integrative Veterinary Health in West Roxbury, MA.

Osteosarcoma is a highly aggressive and malignant form of bone cancer that primarily affects dogs and, less commonly, cats. This type of cancer arises from the bone-forming cells known as osteoblasts and typically occurs in the long bones of the limbs, although it can also develop in the spine, pelvis, and skull. Osteosarcoma is known for its rapid growth and propensity to spread (metastasize) to other parts of the body, particularly the lungs. Understanding the causes, symptoms, and treatment options for osteosarcoma is crucial for pet owners to make informed decisions about their beloved animals' care. In some cases, euthanasia may be considered when the animal's quality of life is severely compromised.

Understanding Osteosarcoma

What is Osteosarcoma?

Osteosarcoma is a type of bone cancer that originates in the bone-forming cells and leads to the production of abnormal, cancerous bone tissue. This cancer is characterized by aggressive growth and a high likelihood of spreading to other parts of the body, most commonly to the lungs. Osteosarcoma is more commonly diagnosed in larger breed dogs. It is rarely seen in cats.

How Does Osteosarcoma Occur?

Osteosarcoma occurs when the normal regulatory mechanisms that control cell growth and division fail, leading to the uncontrolled proliferation of osteoblasts. These cancerous cells form a mass within the bone, causing destruction of healthy bone tissue and weakening the affected area. The exact cause of osteosarcoma is not well understood, but it is believed to involve a combination of genetic and environmental factors.

Who is Affected by Osteosarcoma?

Osteosarcoma can affect both cats and dogs, but certain breeds and ages are more predisposed to the condition:

• Dogs: Osteosarcoma is most commonly seen in large and giant breed dogs. Here are the top 10 breeds more commonly affected:

  1. Great Danes

  2. Rottweilers

  3. Saint Bernards

  4. Irish Wolfhounds

  5. Labrador Retrievers

  6. Golden Retrievers

  7. German Shepherds

  8. Doberman Pinschers

  9. Boxers

  10. Newfoundlands

  Middle-aged to older dogs are more commonly affected, although it can occur in younger dogs as well.

• Cats: Osteosarcoma is relatively rare in cats but can occur in any breed. It tends to affect older cats and is often less aggressive than in dogs.

Causes and Risk Factors

The development of osteosarcoma in cats and dogs can be attributed to several factors:

• Genetic Predisposition: Certain breeds are genetically predisposed to developing osteosarcoma, suggesting a hereditary component to the disease.

• Bone Growth and Size: Rapid bone growth in large and giant breed dogs may increase the risk of developing osteosarcoma.

• Previous Bone Trauma: Previous bone injuries or fractures may increase the likelihood of osteosarcoma development, although this link is not well established.

• Age: Osteosarcoma is more commonly diagnosed in middle-aged to older pets, although it can occur in younger animals.

• Environmental Factors: Exposure to certain environmental toxins or radiation may increase the risk of osteosarcoma, although this is not well understood.

Recognizing the Signs of Osteosarcoma

Understanding the signs of osteosarcoma is crucial for early intervention and management. Common symptoms of osteosarcoma in cats and dogs include:

• Lameness: Affected animals may exhibit persistent lameness or limping, often worsening over time due to bone pain.

• Swelling: Swelling or a noticeable mass may develop at the site of the tumor, often in the limbs.

• Pain: Pets with osteosarcoma may show signs of pain, such as vocalizing, reluctance to move, or sensitivity to touch.

• Loss of Appetite: Affected animals may have a reduced appetite and experience weight loss due to pain and discomfort.

• Fatigue: Pets may appear tired, weak, and less active than usual due to the energy demands of the cancer.

• Fractures: Pathologic fractures, or fractures occurring with minimal trauma, can occur due to the weakening of the bone by the tumor.

Diagnosing Osteosarcoma

If osteosarcoma is suspected, prompt veterinary evaluation is essential. Diagnosing osteosarcoma involves a combination of clinical examination, diagnostic tests, and imaging studies:

• Physical Examination: A veterinarian will assess the pet's overall condition, checking for signs of swelling, pain, and lameness.

• X-rays: X-rays of the affected limb or area can reveal the presence of a bone tumor and assess the extent of bone involvement.

• Biopsy: A biopsy of the tumor may be performed to confirm the diagnosis and determine the type of cancer cells present.

• Blood Tests: Blood tests may be conducted to assess overall health and identify any potential spread of the cancer. Blood tests can be normal in dogs with osteosarcoma, so normal blood work does not rule-out the disease.

• Chest X-rays or CT Scan: Imaging of the chest may be recommended to check for metastasis to the lungs, a common site of spread for osteosarcoma.

Treatment Options for Osteosarcoma

The treatment approach for osteosarcoma depends on the severity of the condition, the location of the tumor, and the pet's overall health. Treatment options may include:

Surgical Intervention

1. Amputation: Amputation of the affected limb is the most common surgical treatment for osteosarcoma in dogs. It can help alleviate pain and improve quality of life, although it does not cure the cancer. Amputation is palliative only, as the cancer has often already spread to the lungs at the time of diagnosis.

2. Limb-Sparing Surgery: In some cases, limb-sparing surgery may be an option to remove the tumor while preserving the limb, although this is less common and depends on the tumor's location and size.

Chemotherapy

1. Adjuvant Chemotherapy: Chemotherapy is often recommended following surgery to help reduce the risk of metastasis and improve survival time. It can help target any remaining cancer cells and slow the spread of the disease.

2. Immunotherapy: Although in the early stages, there recently has been development of immunotherapy treatments to slow the development of osteosarcoma. The most common is the EGFR/HER2 vaccine, which is currently undergoing clinical trials. There have been promising results of slowing the growth and even reversing the growth of pulmonary (lung) metastasis.

Radiation Therapy

1. Palliative Radiation: Radiation therapy may be used to help manage pain and reduce tumor size in cases where surgery is not possible or as an adjunct to surgery and chemotherapy.

Pain Management

1. Pain Medications: Medications, such as non-steroidal anti-inflammatory drugs (NSAIDs) or opioids, may be prescribed to manage pain and improve quality of life.

Palliative Care

1. Supportive Care: Providing supportive care, such as nutritional support and environmental modifications, can help manage symptoms and improve quality of life for pets with osteosarcoma.

2. Alternative Treatments: Acupuncture can be used to reduce pain and alleviate symptoms of malaise from both the cancer and side-effects from chemotherapy.

Prognosis and Quality of Life

The prognosis for osteosarcoma depends on several factors, including the severity of the condition, the location of the tumor, the presence of pre-existing conditions, and the pet’s response to treatment. With appropriate management, some pets with osteosarcoma can lead comfortable, fulfilling lives, although their lifespan may be limited. Osteosarcoma is almost always a terminal diagnosis, with a high likelihood of metastasis to the lungs and other organs. However, new treatments, such as the EGFR/HER2 vaccine, may improve both quality of life and survival time.

When Osteosarcoma Can Be Deadly

While many cases of osteosarcoma can be managed effectively, there are situations where it can become life-threatening:

• Metastasis: Osteosarcoma is known for its high potential to spread to other parts of the body, particularly the lungs, which can lead to life-threatening complications.

• Severe Bone Pain: The aggressive nature of osteosarcoma can cause significant bone pain and discomfort, affecting the pet's quality of life.

• Pathologic Fractures: Weakened bones due to tumor involvement can lead to fractures with minimal trauma, causing severe pain and immobility.

• Respiratory Distress: If the cancer has metastasized to the lungs, it can lead to respiratory distress and potentially life-threatening complications.

Euthanasia Considerations

Euthanasia is a difficult and deeply personal decision that pet owners may face when their beloved animal's quality of life is severely compromised. While osteosarcoma alone is not typically a reason for euthanasia, there are situations where it may be considered:

1. Unmanageable Pain and Suffering: If a pet is experiencing unrelenting pain, suffering, and distress that cannot be alleviated through medical treatment, euthanasia may be a compassionate choice.

2. Poor Prognosis: If the prognosis is poor, and there is little hope for improvement despite aggressive treatment, euthanasia may be considered to prevent further suffering.

3. Severe Complications: If osteosarcoma has led to severe complications that significantly impact the pet's quality of life and the likelihood of recovery is minimal, euthanasia may be an option.

4. Chronic Illness: Pets with chronic or recurrent osteosarcoma due to underlying genetic factors may face ongoing challenges, and euthanasia may be considered when their quality of life is severely diminished.

Making the Decision

Deciding to euthanize a beloved pet is never easy, and it is important for pet owners to have open and honest discussions with their veterinarian about their pet's condition, prognosis, and quality of life. Veterinarians can provide guidance and support to help pet owners make informed decisions about their pet's care.

For those considering euthanasia due to osteosarcoma or other serious health issues, Rough Day Pets offers resources and support to help navigate this challenging time. Our website provides a list of compassionate euthanasia providers to help pet owners find the right professional to assist in making this difficult decision. It's important to remember that choosing euthanasia is a deeply personal decision made out of love and compassion for a pet's well-being.

In conclusion, while osteosarcoma in cats and dogs can be a serious condition, many pets can be managed successfully with appropriate treatment and care. Understanding the signs, causes, and treatment options for osteosarcoma can help pet owners provide the best possible care for their furry companions. In situations where a pet's quality of life is severely compromised, euthanasia may be considered as a compassionate option to prevent further suffering. Pet owners are encouraged to seek support from veterinarians and resources like Rough Day Pets to make informed decisions for their beloved animals.