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Osteosarcoma in dogs

Health & Wellbeing

Have you noticed that your dog is stumbling around, standing strangely or they just seem reluctant to go for a walk when previously they would have jumped at the chance of walkies?

If so, it’s possible that your dog might be suffering from osteosarcoma, which is unfortunately a type of bone cancer that both people and pooches can suffer from. Osteosarcoma is one of the most common types of bone cancers found in dogs, and one of the most severe.

Osteosarcoma in dogs

A diagnosis for any type of cancer is absolutely heart wrenching for any pet parent to hear, and osteosarcoma is typically an aggressive type of cancer that will require carefully monitored and managed treatment to ensure your dog can enjoy a happy life free from pain. We’re going to explain everything you need to know about this devastating disease, why it happens, how to spot it and how it can be managed.

What is osteosarcoma in dogs?

If your dog is suffering from bone cancer, it’s highly likely to be osteosarcoma, as this form of cancer accounts for more than 80% of bone tumours in our dogs. Chondrosarcoma, fibrosarcoma and hemangiosarcoma are other types of bone cancer, although they’re not nearly as widespread as osteosarcoma.

Osteosarcoma can be characterised as a malignant tumour of the bone. When a tumour is malignant, it means it’s aggressive and cancerous, compared to benign tumours, which grow slowly and are non-cancerous.

What areas of the body will osteosarcoma affect?

Osteosarcoma is extremely painful, and most commonly attacks the limbs, which can be referred to as appendicular osteosarcoma. The radius and ulna, which is situated above the front elbow, the ‘forearm’ if we were to think of it as the human body, is the area of the limbs where osteosarcoma typically occurs. Alongside this, the tibia and fibula, located behind the hind knee are commonly affected.

Even though the limbs are the areas usually subjected to osteosarcoma, the axial skeleton, which is comprised of the bones located in the axis (centre) of the body, are also often impacted by the disease. Parts of the axial skeleton that can be affected by osteosarcoma are the skull, spine and ribs.

Although osteosarcoma is a bone cancer, even non-bone tissues can fall victim to the cancer, including the mammary glands, kidneys and liver. This is referred to as extraskeletal osteosarcoma, but it’s reported to be a very rare form of canine osteosarcoma.

What causes osteosarcoma tumours in dogs?

Cancer as a collective disease is constantly being researched and studied, but unfortunately, it still isn’t the best understood. Therefore, there’s not a simple answer as to why your dog might develop osteosarcoma tumours.

We do know that tumours develop through the abnormal, uncontrollable production of cells, which will eventually form together to create a mass (the tumour). The cells that rapidly replicate are called osteoblasts and osteoclasts, and they’re the things that both construct and break down the bones. The tumour is created deep within the bone by the rapid production of those abnormal cells, becoming more and more painful as time goes on as the tumour continues to grow and obliterates the bone from the inside out.

It can form as a primary bone cancer, which refers to a cancer that started in the bone, rather than infiltrating and infecting the bone from somewhere else. When cancer spreads in this way it’s called metastasizing. If the cancer occurred through metastases, it’s referred to as secondary bone cancer.

One definite cause for osteosarcoma isn’t known, but genetics seem to play a role in certain dog breeds developing this type of bone cancer.

What dog breeds are prone to developing osteosarcoma?

It appears to be that large and giant dog breeds are genetically predisposed to developing osteosarcoma, such as:

  • Doberman Pinscher
  • Boxer
  • Golden Retriever
  • Labrador
  • German Shepherd
  • Irish Wolfhound
  • St Bernard
  • Rottweilers
  • Weimaraners
  • Great Danes

This isn’t a complete list, osteosarcoma can impact any breed of dog, this list is just some of the breeds that are commonly reported to suffer from osteosarcoma. Studies have shown that there is some correlation between a dog carrying a lot of body mass and developing bone cancer at some point.

Also, middle aged to senior dogs are the much more likely to develop osteosarcoma over younger dogs and puppies.

What are the signs and symptoms of osteosarcoma in dogs?

As with any type of cancer, if you can catch osteosarcoma early, your dog’s treatment is much more likely to be successful. Keep an eye out for the following signs and symptoms, especially so if you’ve got a dog breed predisposed to osteosarcoma. The most common signs of the disease include:

  • Lameness (dog standing abnormally)
  • Reluctance to get up, walk, exercise and play
  • Lethargy
  • Swelling that feels hard to touch
  • Swollen area might feel hot because of the inflammation
  • Dog showing visible evidence of pain when you touch the affected area
  • Change in demeanour
  • Restlessness and seeming on edge
  • Shaking and shivering
  • Loss of appetite

Dogs are tough, they’ll go out of their way to try and mask any discomfort they’re feeling from their owners, not wanting to outwardly show that they’re in pain. Sadly, these courageous traits mean that the disease can go undetected for quite some time.

Look out for the subtler signs of osteosarcoma, such as a loss of appetite, restlessness and an overall change in personality. You know your four-legged friend better than anyone, so you’ll be able to see if they’re acting out of character. If you’ve got any worries or suspicions, take your dog to get checked out by the vet immediately.

How is osteosarcoma in dogs diagnosed?

If your dog is showing obvious signs of osteosarcoma, such as lameness, swelling and visible discomfort, your vet may already be suspecting bone cancer.

To start a proper diagnosis, an x-ray will be carried out, which should reveal the tumour. Lytic lesions can form from osteosarcoma tumours, which means parts of the bone have worn away, giving a moth-eaten appearance. This happens due to the build-up of cancerous cells breaking down the normal bone tissue.

Also, when tumours have formed in the bone tissue, the bone weakens and becomes susceptible to major breakages from really minor injuries. This is called a pathological fracture, and evidence of this fracture might be the finding that confirms that there is some sort of bone tumour. X-rays can provide your vet with a relatively solid assumption that the tumour is osteosarcoma, but more tests will need to be performed to get a definite diagnosis.

Once some kind of lesion has been found, a sample may need to be taken using a fine needle aspiration, which is essentially just the process of using suction to obtain a sample of the cells directly from the lesion. These samples will then be analysed under a microscope.

Although, this test may not always provide an accurate diagnosis, which is when a bone biopsy will need to be taken. This involves taking small pieces of the affected bone away for testing. Several tests may need to be conducted to accurately diagnose osteosarcoma, work out how aggressive it is and decide on the next steps to take regarding treatment.

Osteosarcoma is an extremely aggressive cancer. Sadly, once a diagnosis has been made, it’s likely that the cancer will already be advanced and started to metastasise. Although it might be undetectable in the initial tests, if the cancer has metastasised, it means the cancer cells have already spread to various other parts of the body.

To check if and how far the cancer has spread, further tests will be conducted, which is a process called staging. This can involve bloodwork, urine tests, further x-rays and ultrasounds.

How is osteosarcoma in dogs treated?

Sadly, it’s usually not possible to fully cure osteosarcoma. Treatment is mainly focused on providing your dog with an extended life expectancy where they’re living happy and pain free. Luckily, there are a few treatment options that you can take to achieve this. With the right monitoring and maintenance, you can help your dog continue living the happy, healthy life that they deserve.

Surgery

To begin, your vet will want to focus on controlling and hopefully removing the initial tumour that started the problem so that it doesn’t spread any further. Surgery is almost always the first step for treating osteosarcoma, and it usually proves to be the most effective. There are two options for surgery, and your vet will be able to guide you here on which is best suited for your dog.

Amputating the affected limb is the most common surgical route to take if your dog is suffering with appendicular osteosarcoma. Of course, this is a distressing thought that no pet parent wants to resort to, but it’s unfortunately the best shot at beating osteosarcoma for most. The majority of the canine population are resilient, brave and extremely adaptable, so they’ll do really well after amputation, quickly re-learning how to navigate the world in this new way.

Limb sparing surgery is also an option, which involves removing the tumour while managing to keep the limb intact. Similar techniques used for humans have been adapted to be used for our canine friends, which involves totally removing the tumorous bone and rebuilding it using bone graft.

This probably sounds like the preferable option, but it isn’t a viable choice for every dog’s situation, and it unfortunately has quite a high rate of complication. Following the surgery, your dog becomes much more susceptible to infection, with a study reporting that 30-50% of dogs who encountered limb sparing surgery subsequently experienced an infection.

Chemotherapy

Post-surgery, a course of chemotherapy will most definitely be administered to continue controlling and minimising the disease for as long as possible.

Chemotherapy is essentially just the overarching term for using drugs to combat cancer, it works to destroy and shrink the cancer cells which should hinder the spread and alleviate symptoms. Even though the aim for surgery is to totally remove the cancerous tumour, there’s a high chance that the cancer had already metastasized (spread to other locations and attached) throughout the body, making chemotherapy a crucial aspect of osteosarcoma treatment.

Unlike humans, dogs don’t experience the side effects of chemotherapy as intensely, any side effects such as vomiting, diarrhoea and a lack of appetite will be minor or non-existent.

Radiation therapy

Radiation therapy, or radiotherapy, is another possible route to go down for your dog, which involves radiation being administered in short bursts over several weeks to kill the osteosarcoma cells.

Cancerous cells don’t have a very good defence system against radiation, unlike normal, healthy cells which can combat it well. By carrying out radiation therapy over a number of weeks, it slowly kills the cancer cells while giving the healthy cells chance to recover from the radiation exposure. This is again used to treat metastasis after surgery.

All these treatment methods have one goal, to get rid of the pain cancer causes alongside maintaining a good quality of life for your dog. You and your vet need to be in a constant open discussion about the right route to take for your pet, so you can make sure you’re always doing the best thing for your dog.

What’s the outlook for my dog with osteosarcoma?

Dogs with osteosarcoma unfortunately don’t have the best prognosis, it’s a severe, aggressive type of cancer that spreads rapidly through the body. However, there’s still plenty of reason to be hopeful, surgery and subsequent pain management and medication can prove lifesaving if you can catch the cancer in its early stages. Your dog’s outlook will all depend on how aggressive the tumour is, how far throughout the body it’s spread and how it behaves after treatment.

Recap

If you’re aware of osteosarcoma, especially if your dog is a breed susceptible to the disease, you can provide your dog with a much better chance of beating the cancer by detecting it in its earliest stages.

Nobody wants to even consider the idea of their dog getting cancer, but if you know the signs and catch it early, you’ll be doing the best thing for your four-legged friend. If your dog is unfortunate enough to get a diagnosis, seek treatment quickly to allow your dog to continue enjoying the happy, healthy life that they deserve.

Sources
  1. What do we know about canine osteosarcoma treatment? Veterinary Research Communications, 39, (1), Nov 2014, 61-67, doi:10.1007/s11259-014-9623-0
  2. Limb-sparing treatment for osteosarcoma in dogs Journal of the American Veterinary Medical Association, 195, (12), Dec 1989, 1734-1744
  3. Demographic characteristics, site and phylogenetic distribution of dogs with appendicular osteosarcoma: 744 dogs (2000-2015) PLOS One, Dec 2019, doi.org/10.1371/journal.pone.0223243
  4. Canine Extraskeletal Osteosarcoma and Chondrosarcoma: a Clinicopathologic Study of 14 Cases PDF Veterinary Pathology, 27, 1990, 46-55
  5. Breed-Predispositions to Cancer in Pedigree Dogs ISRN Veterinary Science, Jan 2013, doi:10.1155/2013/941275