Osteosarcoma - The #1 bone cancer in dogs (what you need to know)

Osteosarcoma is undoubtedly the most common primary bone cancer in dogs ('primary' refers to cancer originating in the bone), accounting for up to 85% of all primary bone tumors in dogs. Since osteosarcoma is so common, I wanted to share which dogs are most commonly affected, how it is diagnosed, as well as the prognosis we can expect with various treatment options.

What is osteosarcoma?

As mentioned above, osteosarcoma is a type of cancer that originates in the bone. It both destroys normal bone and produces new bone, which is very unstable.

Due to the instability caused by the tumor (and often microfractures that develop within the bone) it is an exceedingly painful disease to have.

Commonly, a dog with osteosarcoma will limp due to the destruction that the tumor causes within the bone. Since everything else is normal with the dog, the owner will usually attribute the limp to recent 'rough play' or 'jumping out of the truck'.

Then, when rest and pain meds don't resolve the limp, x-rays of the limb will be taken and reveal significant changes to the bone, caused by the tumor.

As you can imagine, this is usually a shocking experience for the family because they were suspecting an injury caused by playing too hard or jumping out of the truck.

Which dogs are most at risk for osteosarcoma?

Osteosarcoma most commonly affects middle-aged to older dogs with a median age of 7 years (half being older and half younger). There is a small percentage of dogs that will develop the disease at a young age, 18-24 months.

This is generally a disease of large to giant breed dogs. This population tends to develop the disease in the extremities (forelimbs or hindlimbs). Increasing height and weight tend to be the most predictive factors in disease development.

Only 5% of osteosarcoma occurs in dogs weighing less than 33 pounds, but the majority (59%) of these small dogs develop the disease in smaller bones such as the ribs or skull; for smaller dogs, it is uncommon for osteosarcoma to affect a long bone.

In the United States, the breeds most at risk for osteosarcoma include Irish setter, Doberman pinscher, German shepherd, Great Dane, Saint Bernard, golden retriever, Irish wolfhound, greyhound, Rottweiler.

There does appear to be a polygenic (multiple gene) mode of inheritance in certain dog breeds. Research is ongoing to determine how to improve survival/prognosis using this information.

In one study, Rottweilers that were spayed/neutered prior to 1 year had a 25% lifetime risk for developing bone sarcoma and were significantly more likely to develop bone sarcoma than intact (not spayed/neutered) dogs.

What are the signs of osteosarcoma?

As mentioned above, the most common sign of osteosarcoma is limping. It's typical for the history to include an event that was thought to precipitate the limping such as 'jumping out of the truck' or 'rough play', but this has nothing to do with tumor development.

It's important to realize that dogs with osteosarcoma will normally just limp even though they are experiencing a significant amount of pain. They do not vocalize. A dog limping from osteosarcoma is usually severely undermedicated - you should think about these dogs as being as painful as having a fractured leg (and think about what type of pain medication you would want with a fracture - probably more than just Advil).

In fact, I have even seen dogs with bone fractures from osteosarcoma who just limp (eat normally, follow their owners around loyally as always, don't otherwise complain) - the only way that we knew the bone was broken was by taking a radiograph (x-ray). It's always slightly horrifying to think about the amount of pain they were tolerating.

How do we make a diagnosis?

In most cases, we become very suspicious of osteosarcoma based on a combination of the x-ray findings (classic changes to the bone as well as the specific location of the bone affected) and signalment of the patient (breed, age).

Most oncologists want to be certain of their suspicion by obtaining a diagnosis before beginning treatment. In most cases, this is typically pretty easy and can be done with a needle aspirate. This will give you a diagnosis in 97% of cases. Sometimes the pathologist will give you a diagnosis of 'sarcoma' instead of 'osteosarcoma', but this is considered close enough.

An aspirate DOES NOT increase the chance of bone fracture. We are using a small needle. I've done a ton of these and have never had a fracture nor have I ever heard of a colleague that has caused a fracture from a bone aspirate.

There are some cases where the bone looks pretty normal (not much destruction) but we still suspect osteosarcoma. In these cases, I'm less confident about the needle being adequate for sampling (as you can imagine, a small needle will not go through hard normal bone). In these cases, we will recommend a bone biopsy. A biopsy takes a larger piece of bone, gives you more information, but there is a risk of fracture. These are all things that can be discussed with your oncologist.

There are definitely exceptions and situations where we might be okay just going to surgery and skipping the diagnosis part:

(1) If the bone is fractured, usually surgery or euthanasia are considered the only two reasonable options. In this case, surgery is recommended, as long as the family accepts that we don't have a diagnosis and prognosis is unknown. The goal of surgery alone is palliative (will relieve pain, but will not otherwise treat the tumor).

(2) Sometimes a family understands that their dog is extremely painful and just wants surgery (amputation) to improve comfort. They accept that we suspect osteosarcoma, but understand that their dog may have a different type of cancer or even a fungal disease (depending on where they live). They will get a diagnosis after the bone is sent to the pathologist, but their main goal is to help their dog feel better quickly. They will decide on treatment once the tumor has been processed (after surgery).

What is the recommended workup for osteosarcoma?

Another way to describe the workup is by saying 'staging'. The following paragraphs describe the staging tests that are typically needed for an osteosarcoma patient. Staging basically means looking throughout the body for evidence of tumor spread (metastasis) but also establishing the overall health of the patient.

The typical workup includes full blood work (complete blood count, chemistry panel) with a urinalysis - this is to help establish the overall health of the liver, kidneys, etc.

Three-view thoracic radiographs (chest x-rays) that are reviewed by a radiologist are also needed to ensure that the heart appears normal and there is no obvious evidence of cancer in the lungs. You always want a radiologist making the final decision as to whether there is obvious cancer in the lungs - it typically costs an extra $60-$80 and is well worth it.

In osteosarcoma, we will only find obvious lung nodules (spread of cancer to the lungs) in 10-15% of cases at diagnosis. If found, the prognosis is typically significantly worse (we usually say 1-3 months on average). Some dogs do better than this and of course, there is the option to treat with chemotherapy to help slow down the disease in the lungs.

If there is only one lung nodule, and it is growing slowly, a metastasectomy (removing the lung lobe with the nodule) could even be explored for the family that wants to be as aggressive as possible.

It's important to know that even if the chest x-rays are 'clean' (no obvious cancer), in 90% of cases, microscopic cancer cells have already spread there, we just can't see them. This is why we don't cure osteosarcoma with surgery (amputation) and why chemotherapy is always recommended for the best outcome.

For a middle-aged to older patient, I also recommend an abdominal ultrasound before surgery/deciding on a treatment option. It is unlikely for osteosarcoma to spread (metastasize) to an abdominal organ (if it does, the prognosis (expected lifespan) is generally less than 2 months). Sometimes when we perform an abdominal ultrasound, we find 'silent' diseases (such as a tumor in the spleen) that may affect the lifespan and may change the decision to proceed with treatment.

I think of ultrasound as a way to increase the chance of helping your dog achieve the expected outcome with the treatment option you've chosen. I've seen people spend $5000 on surgery, only to lose their dog to a bleeding tumor in the spleen 2 months later, that they didn't know was there (but would have if they did the ultrasound). Those situations are the absolute worst.

Lastly, if the lymph node is enlarged on the same leg as the tumor, it should be aspirated (sampled) - the prognosis is significantly shorter if cancer has spread to the lymph node (just a few months).

In some cases, an oncologist might recommend other tests that aren't listed above (ex: if a dog has a heart murmur they might recommend an echocardiogram prior to surgery).

Treatment options and associated prognoses:

How long will a dog live with osteosarcoma? Well, it depends on which treatment option is chosen.

I've listed the most common treatment options below. Talk to an oncologist to see what is appropriate for your dog and for more details for each option.

(1) Amputation alone:

Amputation sounds a bit awful because we anthropomorphize. Provided that a dog is otherwise orthopedically sound and not obese, they typically do extremely well with an amputation.

In many cases, the dog is not using the affected leg before surgery and is effectively 3-legged already. These patients tend to get up the day after amputation without a problem.

If you've never seen a 3-legged dog run or swim, check out YouTube. Many clients report that they wish they amputated sooner because their dog feels so much better.

With amputation alone, a dog with osteosarcoma will live an average of 4-6 months. This is because amputation simply relieves pain and improves quality of life - it does nothing to slow the tumor down.

After 4-6 months, patients typically succumb to pulmonary metastasis (spread of cancer to the lungs) if they are not receiving chemotherapy.

Note: There are some cases where a prosthetic can be considered to help support a patient after surgery. The vast majority of dogs will not need this. Typically this needs to be planned before surgery and in most cases is restricted to cases where the tumor is near the wrist/ankle. One company (aocpet.com) has created a brace for full leg amputees, but I do not have information on how well they feel it is working.

(2) Amputation + Chemotherapy

This is considered gold standard treatment. Amputation relieves the painful tumor and 4-6 doses of carboplatin chemotherapy delays the spread of osteosarcoma to the lungs. Adding chemotherapy after amputation increases expected survival from 4-6 months to 10-12 months.

During chemotherapy we expect patients to feel well (chemo is vastly different in dogs than in people). If they don't feel well, we make a change. We treat patients so that they can have a good quality of life, despite having cancer.

During treatment (and after chemo is finished), chest x-rays are taken at routine intervals to assess for metastasis (spread of cancer to the lungs). If/when metastasis is noted, a different type of chemotherapy can be pursued in an attempt to slow down metastasis.

(3) SRT (stereotactic radiation) + carboplatin + zoledronate

For people that are opposed to amputation (or in situations where a dog is not a candidate), stereotactic radiation (SRT) can be used to reduce bone pain and kill cancer cells.

Some dogs will walk normally after this treatment, some will still limp. Most still require oral pain meds. Dogs are still at risk for fracture after this treatment.

SRT involves a CT scan for radiation planning, then 1-3 treatments of radiation therapy. Each of these requires anesthesia.

This type of radiation improves pain, allowing dogs to live longer. If they also receive carboplatin chemotherapy (and often monthly zoledronate injections to help reduce bone turnover), dogs can live for one year (sometimes more and sometimes less).

They do not become "sick" from radiation and the radiation usually does not typically cause skin side effects, with the exception of skin irritation (discuss this specifically with your radiation oncologist to determine what side effects they typically see with radiation "in their hands").

(4) Palliative radiation therapy + pain meds

Palliative radiation will reduce (not eliminate) bone pain for 2-4 months. This should improve quality of life for dogs with osteosarcoma. This is a good option for people that don't elect amputation and for those that cannot afford SRT (or don't have it nearby).

A radiation oncologist will either require an x-ray or CT scan to plan for radiation. They then receive approximately 5 or 6 radiation treatments. Sometimes all of the treatments are done in a week, sometimes once per week, etc (every radiation oncologist has their favorite protocol).

This type of radiation improves bone pain. It doesn't make pets feel "sick" and doesn't cause significant skin side effects (possibly some skin irritation or redness).

If this option is elected and is effective, you will still have to continue with oral pain medications, but might be able to reduce the amount that you are giving.

If it works well, there is the option to repeat the treatment when it wears off (in 2-4 months), although that becomes costly.

(5) Pain medication only

I would say that patients with osteosarcoma are the most inappropriately under-medicated group of patients that I see.

We have to treat them as if they are as painful as having a fractured leg, and understand that if they're limping, they're painful (even though they're not vocalizing - don't expect them to act like we would).

These patients should be on a good combination of an NSAID (such as carprofen/Rimadyl/meloxicam/Galliprant), gabapentin, amantadine, and possible CBD oil or acupuncture.

If they are painful despite these interventions or become acutely more painful, take another x-ray to ensure that the bone has not fractured. If no evidence of fracture, you can consider placing a new fentanyl patch on the skin every 5 days (this is a very strong pain medication).

Try to prevent weight gain, as this will make life more difficult/painful for them.

I would say that on average, a patient receiving oral pain medication alone may live 2-3 months. They should live for as long as we feel that we are reasonably controlling their pain. They may still eat and have many normal behaviors, but if they are not weight-bearing on the affected limb, they are probably not loving life due to a great deal of pain. In this case, a visit with the vet is in order to discuss whether euthanasia is appropriate.

(6) Future treatments

Amputation + chemotherapy + osteosarcoma vaccines seem to be the future for canine osteosarcoma. There is currently one of these vaccines under investigation, which targets HER2/neu. It has shown initial promise, resulting in a median survival of approximately three years when combined with amputation and chemotherapy. The trial has closed; current trial participants are being followed to see how well they do. Once enough information has been gathered the study will be published.

A vaccine targeting EGFR/HER2 (Yale - Dr. Mamula) was recently pulled due to a USDA licensing issue. Published information on its efficacy is not available but many dog owners report improvement in lung metastasis.

What if there is lung metastasis?

If your dog has lung metastasis and you want to proceed with treatment, there are usually a few options.

(1) If there is only 1 nodule, growing slowly, removing it (and the associated lung lobe) then following with chemotherapy can be considered.

(2) Chemotherapy can be considered to slow down cancer in the lungs. This may or may not help. Your oncologist would take periodic chest x-rays to determine if chemotherapy is helping.

(3) There might be a clinical trial exploring the treatment of metastatic osteosarcoma that your dog could enter.

(4) Every case is different. Discuss the LATEST options with your oncologist - these things change all of the time. Immunomodulatory treatment with oral medications (including Palladia) seem to be the next frontier.

What are the biggest misconceptions to be aware of?

(1) "Your dog is too big for an amputation"

If you hear this from a veterinarian that is not a surgeon or oncologist, get a second opinion from an oncologist. We perform amputations on large/giant breed dogs all of the time (those are the dogs that get this disease, remember?) and the dogs are happy and so are their owners.

Prior to the amputation, the oncologist will have a surgeon perform an orthopedic/neurologic exam to ensure your dog will do well on 3 legs.

Note: if your dog is already walking only on 3 legs, you know he'll be fine with only 3 legs after surgery.

(2) "My dog isn't painful - he's eating and not vocalizing"

That's great, but if he's limping, he's painful. Dogs express pain differently than we do. Don't expect them to vocalize, they won't, they're just going to limp. They might just have a mild limp, not because they're not very painful, but because the other leg has arthritis or a cruciate tear, so they're compensating the best they can.

Talk to your vet/oncologist about what you can do for pain, and use the guidelines above. Remember that the only 100% reliable way to eliminate pain is to remove the tumor with an amputation.

(3) "Amputation is cruel"

I understand that this surgery is a bit hard to wrap your head around, but remember, dogs are not people. They're not going to miss their leg, they'll just know they're not painful anymore.

If it helps, talk to someone that has a dog with osteosarcoma that has undergone amputation. I suspect they'll tell you they were shocked at how fast their dog recovered and that they regret not having the surgery performed sooner.

Want the best experience? Have surgery done by a board-certified surgeon that performs amputations every week, at a clinic that has 24-hour care and will keep your pup overnight for appropriate pain management and monitoring.

I hope you found this article helpful. If you know someone with a large breed dog that might benefit from this information (or that has a dog with osteosarcoma), feel free to pass it along.

Dr. Lori Cesario

Board Certified Veterinary Oncologist

PS: I'm happy to now offer online oncology consultations. Learn more about how this service can help by visiting the Vet Cancer Consultants site.

A few other articles you might enjoy...

(1) Dog Breeds and Their Associated Cancers

(2) A Great Resource for Herbs & Supplements

(3) How To Tell If Your Dog is Nauseous

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