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Bone cancer or osteosarcoma is an aggressive cancer that can rapidly progress and cause immense suffering in dogs. When your beloved companion receives a canine osteosarcoma diagnosis, understanding the stages of osteosarcoma in dogs can help you make informed treatment decisions about their care and quality of life.

Stages of Osteosarcoma in Dogs

Osteosarcoma in dogs can manifest with early signs such as swelling or a mass at the cancer site, lameness, limb pain, changes in appetite, weight loss, and lethargy. As the disease progresses, these early-stage symptoms can persist and worsen, potentially leading to diarrhea, increased limb swelling, ruptured skin, or a pathologic fracture, with paralysis occurring if the spine is involved. A dog with osteosarcoma may also experience seizures, collapse, or profuse bleeding.

Aggressive osteosarcoma in dogs often presents with subtle early signs that can rapidly worsen. Our veterinary team can support you with a quality-of-life evaluation or comfort care appointment to help assess when treatment is no longer bringing relief, and whether hospice or euthanasia may be the most compassionate next step.

Progression of Osteosarcoma in Dogs

Stages of progression of canine osteosarcoma exist because this aggressive cancer, particularly prevalent in giant breed dogs, is highly prone to early lung metastasis. This dictates different clinical presentations and prognoses as the disease advances.

1. Early Stages

The primary risk in the early stages of canine osteosarcoma is the high likelihood that most dogs already have a microscopic spread of the disease that manifests in the form of:

Swelling or mass at the site of cancer
Lameness and/or limb pain
Change in appetite
Weight loss
Licking the affected area
Tender to the touch
Lethargy
Exercise intolerance

2. Final Stages

The effects can be more difficult to manage in the last stages of aggressive bone cancer. This is why treatment options for appendicular osteosarcoma in dogs primarily focus on palliative care to manage pain and increase comfort. The primary change in prognosis is usually based on whether metastasis is detectable (especially in the lungs). During this phase of the disease, we notice more persistent pain, reduced mobility, signs of fatigue, possibly starting to affect breathing if metastases have grown as well as:

Persistent early stages
Non-weight-bearing lameness
Vomiting and or/diarrhea
Affected limb swelling/edema
Ruptured skin over the site/infection
Pathologic fracture
Difficulty breathing/coughing
Unable to stand
Paralysis if the spine is involved

3. Crisis Stage

During the crisis stages of canine osteosarcoma, unforeseen complications can severely impact your dog’s quality of life and necessitate immediate veterinary intervention. During this stage, we see: Severe pain, inability to walk, labored breathing, major decline in quality of life, this is often when euthanasia is considered.

Difficulty breathing
Prolonged seizures
Uncontrollable vomiting/diarrhea
Sudden collapse
Profuse bleeding – internal or external
Crying/whining from pain*

*Most animals will instinctively hide their pain. Vocalization of any sort that is out of the ordinary for your pet may indicate that their pain and anxiety have become too much for them to bear. If your pet vocalizes due to pain or anxiety, please consult with your veterinarian immediately.

Osteosarcoma in Dogs

Bone cancer or osteosarcoma (OSA) is the most common bone tumor in dogs and can sometimes be present in cats. Osteosarcoma develops deep within the bone and becomes more painful as it grows outward, destroying bone as it progresses.

Obvious swelling becomes evident as the tumor grows and normal bone is replaced with cancerous bone. Cancerous bones are not as strong as normal bones and can break with a minor injury. This type of broken bone is called a “pathologic fracture”, which strongly suggests the presence of cancer cells.

Dog Breeds Prone to Osteosarcoma

Canine osteosarcoma usually occurs in the leg bones of large and giant breeds. While small-breed dogs are less likely to develop osteosarcoma, they tend to survive longer than giant-breed dogs. The most common sites are the long bones of the limbs, especially the distal radius, proximal humerus, and distal femur/proximal tibia. These are areas of rapid bone growth, which is why large breeds are at higher risk.

Due to genetics and environmental influences, predisposed breeds or breeds with a high risk of developing osteosarcoma include:

Boxer
Great Dane
Rottweiler
Saint Bernard
Irish Setter
Doberman Pinscher
Greyhound
German Shepherd
Irish Wolfhound
Leonberger

Parts of the Canine Body Affected by Osteosarcoma

Canine appendicular osteosarcoma is an aggressive type of cancer that can develop in any bone, although the legs account for 75% to 85% of affected bones. Most dogs with bone tumor cells can experience pain in these skeletal parts:

Proximal humerus (the part closest to the shoulder)
Distal femur (the part closest to the knee)
Distal radius (the part closest to the wrist)
Proximal and distal tibia (both ends of the shin bone)

Causes and Risk Factors of Osteosarcoma in Dogs

Like most cancers in animals, the exact cause of canine osteosarcoma is unknown. However, genetics, environment, and lifestyle factors can increase the risk of appendicular osteosarcoma in dogs.

Endogenous gonadal hormone exposure is the natural production and circulating levels of sex hormones. While spaying and neutering contribute to controlling the canine population, studies suggest that early gonadectomy may increase the risk of canine osteosarcoma due to these reasons:

Spaying or neutering before a dog has fully matured can delay the closing of their growth plates, especially in large and giant breeds.
Hormonal imbalance may disrupt bone growth and remodeling as they age.
Dogs with weaker bones may feel more stress on their bones because of an increased body weight.

Common Signs of Pain in Canine Osteosarcoma

Bone cancer can be extremely painful, and most dogs with appendicular osteosarcoma can show these warning signs:

- Panting
- Lameness
- Difficulty sleeping
- Pacing
- Abnormal posture
- Body tensing
- Poor grooming habits
- Tucked tail
- Dilated pupils
- Licking the sore spot
- Muscle atrophy
- Decreased appetite
- Vocalizing/yowling
- Reclusive behavior
- Aggressive behavior
- Avoiding stairs/jumping
- Seeming withdrawn or down
- Unable to stand

Diagnosing Osteosarcoma in Dogs

Osteosarcoma is often diagnosed via radiographs (X-rays) as it usually has a distinctive pattern. However, a definitive diagnosis is made by bone biopsy. A vet may use a combination of these tests to determine the severity of the canine osteosarcoma. This staging process (determining the disease’s extent) also enables vets to recommend potential treatment and care plans.

1. X-Ray (Radiographs)

As the first step, radiographs provide initial visual evidence of a bone tumor. It reveals characteristic patterns like a lytic (eaten away) appearance within the diseased bone, often, these finding are suspicious for osteosarcoma, prompting further diagnostic steps like biopsy.

2. Advanced Imaging

Nuclear scintigraphy can detect metastatic bone lesions that may not be visible on standard X-rays, making it useful for identifying cancer spread throughout the skeleton. CT (computed tomography) scans provide detailed cross-sectional images, allowing for precise assessment of the primary tumor’s size, location, and involvement with surrounding tissues. However, these tests can be expensive and often will not change the treatment plan for osteosarcoma in dogs.

3. Bone Biopsy

Distinct from imaging, a bone biopsy is the definitive diagnostic procedure for detecting osteosarcoma in dogs. Often used in distal radial osteosarcoma, biopsy involves the direct collection of cells from the lymph nodes for microscopic examination. However, its invasiveness means many veterinarians seek less invasive methods.

4. Fine Needle Aspiration (FNA) With ALP Staining

Fine needle aspiration is a minimally invasive procedure that collects cells from the bone tumor. These cells are then analyzed using alkaline phosphatase (ALP) staining, which helps distinguish osteosarcoma cells from other types of tumors or conditions. This technique provides a reliable preliminary diagnosis and can often confirm appendicular osteosarcoma without needing a more invasive biopsy.

5. Bloodwork

Unlike direct imaging or tissue sampling, bloodwork assesses the dog’s holistic systemic health, identifies potential comorbidities, and provides prognostic markers. The results from full chemistry, complete blood count, and clotting times can influence treatment options for most dogs.

6. Ultrasound (Abdominal)

While chest X-rays are the primary source for detecting lung metastasis, abdominal ultrasound specifically examines organs for metastatic spread. This can also serve as a distinct tool to evaluate the systemic reach of aggressive cancer beyond just canine appendicular osteosarcoma.

Prognosis for Dogs With Osteosarcoma

Unfortunately, by the time canine osteosarcoma reveals itself, it has likely metastasized (spread) to other areas of the body, such as the lungs, other bones, lymph nodes, and internal organs. Despite amputation, about 80% to 90% of dogs that develop lung metastasis due to appendicular osteosarcoma may only have an 11.5% one-year survival rate and a 2% two-year chance of survival.

If osteosarcoma has already spread to the lungs at the time of diagnosis, chemotherapy is often less effective and may only extend the dog’s life by a few months. However, when treatment begins before metastasis is detectable on imaging, chemotherapy can sometimes extend survival to a year or longer.

Signs are dependent on the severity of the disease and whether or not treatment options are elected. A personalized treatment plan is important to slow the progression of appendicular osteosarcoma in dogs. Talk to your veterinarian regarding the best treatment protocol for your pet.

Canine Osteosarcoma Treatment and Pain Management

Treatment of osteosarcoma in dogs has one or two goals: to try to cure the cancer or simply decrease pain and symptoms if a cure is not possible. Managing pain and trying to slow the progression includes the use of pain medicine, radiation therapy, limb amputation, and chemotherapy.

Curative intent options include combining different modes of therapy, such as surgery, radiation therapy, and chemotherapy. However, no matter the combination used, most dogs who develop osteosarcoma ultimately die due to the high metastatic potential of this bone tumor.

When treatment options are no longer effective, providing hospice care or considering euthanasia can be the kindest way to relieve a dog’s pain and ensure their comfort.

1. Surgery

Amputation or limb-sparing surgery is the most common surgical treatment for canine osteosarcoma. This is because there’s no other way to remove the tumor without removing the affected bone. It’s the quickest way to remove the source of pain.

2. Chemotherapy

Cancer cells may likely spread to the rest of a dog’s body, including the lymph nodes and internal organs. This is why chemotherapy often follows limb-sparing surgery. Chemotherapy drugs like pamidronate are often used to kill osteosarcoma cell lines.

3. Palliative Radiation

Palliative radiation is also commonly done after a limb-sparing surgery. This helps reduce symptoms and maintain a dog’s quality of life.

4. Immunotherapy and Vaccine

There’s still hope for dogs with osteosarcoma as vaccines are now being developed and tested for canine osteosarcoma. This includes an autologous cancer cell vaccine that targets cancer cells, with patients having a median survival rate of 415 days.

5. Alternative Therapies and Supplements

Acupuncture and supplements provide pain management for most dogs with osteosarcoma. However, be sure to consult with your vet first about which therapies and supplements can provide pain relief and anti-inflammatory properties to your pet.

6. Hospice

As this metastatic disease progresses further, there may come a time when surgery and pain relief options will no longer work. Hospice can provide adequate pain control as dogs with osteosarcoma live their final days.

Conclusion

Recognizing the stages of canine osteosarcoma enables you to make timely decisions about treatment options, pain control, and the best measures for your dog’s affected limb. This also helps you provide care tailored to your pet’s stage of disease progression. Contact Paws into Grace today to discuss how we can support your beloved pet through this challenging disease with dignity and comfort.

Elizabeth Benson, DVM

Dr. Benson started Paws into Grace in 2007. She wanted to give pets and their parents a beautiful last encounter that didn't have to be in an unfamiliar office where pets were often frightened. The empathy she shows each family creates a lasting impression on them. In her free time, Dr. Benson enjoys running and spending time with her family, dogs, cats, and chickens.

Stages of Osteosarcoma in Dogs