Understanding Osteosarcoma in Dogs

Getting a diagnosis of osteosarcoma can feel like the ground shifting beneath you. It’s one of the most serious cancers dogs face, and the word itself can be frightening. But understanding what this disease is, how it behaves, and what your options look like can help you feel more grounded as you figure out the next steps. Whatever stage of this journey you’re on, you don’t have to navigate it alone.

What is osteosarcoma in dogs?

Osteosarcoma is a malignant bone cancer formed from abnormal production of specific cells in bones that are intended to create and break down bone. It’s also the most aggressive, and unfortunately the most common. Osteosarcoma accounts for 80 to 90% of canine primary bone tumors.

It’s most often diagnosed in large or giant breed dogs, such as Rottweilers, Great Danes, St. Bernards, and Golden Retrievers, and the tumor commonly grows on the long bones of the forelimbs or hindlimbs, causing pain and lameness. In the US, more than 10,000 dogs are diagnosed with osteosarcoma each year.

This is a very aggressive tumor and often spreads to the lungs early in the disease. Often, at the time of diagnosis, the tumor has already spread to the lung, whether those lesions are visible on radiographs or not. This is one of the things that makes osteosarcoma so hard to treat, and why early detection matters as much as it does.

Symptoms of osteosarcoma in dogs

The earliest signs are easy to miss, or to chalk up to aging or a minor injury. If your dog is a large or giant breed, any persistent lameness is worth taking seriously.

Here’s what to watch for:

• Limping or lameness, especially on a front leg, that doesn’t improve with rest
• Swelling around a limb or joint that appears gradually
• Pain when touching the affected area, your dog may flinch or pull away
• Reluctance to exercise, play, or go up stairs
• Loss of appetite or weight loss as the disease progresses
• Difficulty breathing, which can indicate the cancer has spread to the lungs

Any lameness in a large-breed dog that does not promptly resolve with symptomatic therapy should be examined by a veterinarian. The sooner it’s investigated, the more options you’ll have.

What causes osteosarcoma in dogs?

The exact cause isn’t fully understood. Body mass is strongly associated with osteosarcoma risk, and dogs over 40 kg show significantly higher odds of developing the disease compared with smaller dogs. Breeds with the highest annual prevalence include the Scottish Deerhound, Leonberger, Great Dane, and Rottweiler.

About 80% of osteosarcoma cases occur in dogs over seven years of age, and it’s rarely seen in younger dogs. Trauma and prior bone injury have also been discussed as potential contributing factors, though the research on this is still developing. As with many cancers, there’s no single cause, and nothing you did or didn’t do caused this.

How is it diagnosed?

If your vet suspects osteosarcoma, they’ll typically start with X-rays of the affected limb to look for characteristic bone changes. From there, diagnosis may involve:

• X-rays of the chest to check for visible spread to the lungs
• A biopsy, a small sample of bone tissue taken to confirm the type of cancer and rule out other conditions
• A CT scan for more detailed imaging, particularly if surgery is being considered
• Blood work to assess your dog’s overall health and suitability for treatment

The biopsy is what confirms the diagnosis definitively. Your vet will walk you through what each step involves and why it’s needed. Don’t hesitate to ask questions at every stage.

Treatment options for osteosarcoma in dogs

There’s no single right answer when it comes to treating osteosarcoma. The best path forward depends on your dog’s age, overall health, where the tumor is located, and what matters most to you and your family. Here’s an honest overview of what’s available.

Amputation with chemotherapy

Amputation to remove the primary tumor, combined with chemotherapy to treat the metastatic disease, is the best treatment for preservation of quality and quantity of life for dogs with the limb form of osteosarcoma. It’s understandably a difficult decision for many owners, but it’s worth knowing that dogs adapt to three legs much better than most owners expect. Most dogs are already not using the affected leg because it’s so painful, so they’ve already begun to adapt. After surgery, they often find immediate relief.

Amputation with chemotherapy brings the average survival time to just under one year, with 20% of dogs still enjoying a good quality of life two years after surgery.

Limb-sparing surgery

For dogs who aren’t good candidates for amputation, limb-sparing surgery is sometimes an option. Limb-sparing surgery combined with chemotherapy does not improve survival times over amputation with chemotherapy, with median survival times of about one year reported. It’s a more complex procedure and isn’t available at all veterinary facilities, so your vet will advise whether it’s appropriate for your dog.

Chemotherapy

Platinum-based chemotherapy agents, such as cisplatin or carboplatin, and doxorubicin are the current standards of care for systemic chemotherapy in dogs with osteosarcoma. Chemotherapy after surgery aims to delay the spread of the disease and is often better tolerated by dogs than many owners expect.

Palliative care

If surgery isn’t an option, or if you’ve decided it isn’t the right choice for your dog, palliative care focuses on keeping your dog comfortable for as long as possible. Options include traditional radiation therapy, stereotactic radiation therapy, bisphosphonate drugs (which inhibit bone destruction and help decrease pain), and aggressive pain management including NSAIDs, gabapentin, and opioids. This is a valid and loving path, and many families choose it.

Emerging treatments

Researchers are also exploring immunotherapy options. Unlike chemotherapy, which aims to kill cancer cells directly, immunotherapy activates the dog’s own immune system to fight the disease. Clinical trials are ongoing, and your veterinary oncologist can advise whether any trials are open to your dog.

Prognosis and what to expect

This is the hardest part of the article to read, and we won’t soften the truth. Osteosarcoma often carries a poor prognosis as it tends to behave aggressively, and there is no cure.

Without any treatment, the average survival time is about two months, and most dogs are not able to bear the pain and discomfort that comes with osteosarcoma much longer than that. When surgery is combined with chemotherapy, the median survival time is about nine months, though individual dogs will vary in their response to treatment. About half of dogs with osteosarcoma treated with surgery and chemotherapy will be alive one year after diagnosis, and approximately 25% will be alive at two years.

That’s difficult news, and it’s okay to take a moment with it. What the numbers can’t tell you is what the time you have with your dog can look like. Some dogs beat the odds. Many have good days, really good ones. Focus on what your dog is telling you, and take it one step at a time.

Using the HHHHHMM scale

When treatment is underway, or if you’ve chosen palliative care, one of the hardest ongoing questions is: how is my dog actually doing? The HHHHHMM scale is a practical tool to help you assess that, and to guide conversations with your vet about quality of life. It stands for:

• Hurt: Is your dog’s pain manageable with current medication?
• Hunger: Are they willing and able to eat?
• Hydration: Are they drinking enough to stay hydrated?
• Hygiene: Can you keep them clean and comfortable, free from sores or matting?
• Happiness: Do they still respond to you, show interest in their surroundings, or enjoy moments of their day?
• Mobility: Can they move around, even a little, without severe difficulty?
• More good days than bad: Taken together, are the positive moments outweighing the painful or difficult ones?

When bad days begin to outnumber the good consistently, it may be time to have a conversation with your vet about what comes next. That’s not giving up. It’s one of the most loving things you can do.

When to consider euthanasia

This is the hardest conversation, and there’s no perfect moment that makes it easier. Signs that it may be time include unmanageable pain despite medication, a consistent refusal or inability to eat or drink, frequent collapse, or a dog who has stopped engaging with the people and things they love.

Your vet is your most important partner here. They’ve had these conversations before, and they can help you think through what your dog is experiencing and what a peaceful, dignified process looks like. You’re not making this decision because you’re giving up. You’re making it because you love your dog, and that love includes knowing when to let go.

Is it covered by pet insurance?

Treatment for osteosarcoma, from diagnostics and surgery to chemotherapy and palliative care, can be significant in cost, and financial stress is the last thing you need when you’re already going through something this hard. If your dog is diagnosed with osteosarcoma after enrolling in a Lemonade Pet policy, those costs can be covered, as long as the condition isn’t pre-existing. That includes diagnostics, surgery, chemotherapy, and follow-up care.

For large and giant breed dogs that are genetically predisposed, getting coverage in place before any symptoms appear is especially important. Once a condition appears in your dog’s medical history, it becomes pre-existing and can’t be covered going forward.

Before we go

An osteosarcoma diagnosis is one of the hardest things a dog owner can face. The speed of it, the weight of the decisions, the grief that starts before you’ve had time to process. It’s a lot, and it’s okay to feel all of it. Lean on your vet, ask every question you have, and give yourself permission to not have all the answers right away. Whatever path you choose, surgery, palliative care, or something in between, it comes from love. And that’s exactly what your dog needs most.

A few quick words, because we <3 our lawyers: This post is general in nature, and any statement in it doesn’t alter the terms, conditions, exclusions, or limitations of the policies issued, which differ according to your state of residence. You’re encouraged to discuss your specific circumstances with your own professional advisors. The purpose of this post is merely to provide you with info and insights you can use to make such discussions more productive! Naturally, all comments by, or references to, third parties represent their own views, and Lemonade assumes no responsibility for them. Coverage may not be available in all states. Please note that statements about coverages, policy management, claims processes, Giveback, and customer support apply to policies underwritten by Lemonade Insurance Company or Metromile Insurance Company, a Lemonade company, sold by Lemonade Insurance Agency, LLC.  The statements do not apply to policies underwritten by other carriers.