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The Cancer Connection in Dogs and Humans

Comparative Oncology: the cure is by our side...

It started with Harry, a seven-year-old Australian Cattle Dog, bounding into the clinic for his annual exam, and ended with dreadful news. Harry – a favourite and especially cheeky patient – had no history of ill health. 

However, during his physical, all his superficial lymph nodes (or glands) were enlarged, and a quick look under the microscope was worrisome. 

Referral to an oncologist confirmed the worst: Harry had advanced multicentric T-cell lymphoma, and in his case, the prognosis was grave. Worse still, a family member had recently passed away from a similar cancer – an awful, tragic coincidence.

It turns out we share much more than our homes and hearts with our pets. Chances are, if you have lived with pets, or know someone who has, you will have been touched by animal cancer. 

Tragically, over a dog’s lifetime, 1 in 4 will develop cancer, and in dogs aged over 10, this increases to 1 in 2. 

In cats the numbers are similar: 1 in 5 will develop cancer over their lifetime, jumping up to 1 in 3 in cats over 9 years of age. This may be an underestimate as cats are less likely to visit the vet.

Pet dogs and cats, and humans, develop cancer at the same rate, and in many cases, the cancers are just the same: they are diagnosed in the same way, treated with the same therapies, and share the same outcomes or prognoses. As just one example, dogs are the only non-human species that develop prostate cancer. Pet cats and women both suffer the most treatment-resistant and deadly of all breast cancers, the triple negative form.

Comparative Oncology is an exciting field of research comparing cancer in humans and in our amazing companion animals, dogs and cats. By studying the remarkable similarities between humans and our pets – in the development, progression, and treatment of cancer – we gain insights that benefit all of us. 
Note: this research occurs in pets in the community, not in colonies of animals in the laboratory.

Cats and dogs are invaluable models for comparative oncology because they naturally develop cancer, including many of the same types found in humans: lymphoma, like in Harry’s case; bone cancer (osteosarcoma); melanoma and other skin cancers; bladder cancer; head and neck cancer; brain and lung cancers; leukemias and soft tissue sarcomas; as well as less common cancers.

Non-Hodgkin's lymphoma (NHL) is a cancer affecting the body's immune system. In humans, NHL is the seventh-most common type of cancer, affecting people of all ages. 
In dogs, NHL is even more common, making up 20% of all canine cancers, mostly occurring in middle-aged dogs. 

A Boxer is being treated for cancer at a veterinary clinic in the USA

There may be a genetic susceptibility: it is most prevalent in breeds such as Golden Retrievers, Boxers, Bulldogs, Dobermann Pinschers, Rottweilers, Bernese Mountain Dogs, German Shepherds, Scottish Terriers, and Basset Hounds. 

Canine NHL originates within tissues of the immune system and can spread to different organs, including lymph nodes, liver, spleen, bone marrow, and the gastrointestinal tract. 

Credit: Animal Cancer Foundation (Facebook)
The causes of NHL in dogs are unclear, but may include genetic factors, ageing of the immune system, and exposure to certain environmental pollutants and chemicals.

Treatment options for NHL in humans and dogs are very similar but may vary in approach. In both cases, treatment typically involves a common chemotherapy protocol, and may be combined with radiation therapy or surgery.

Some exciting new treatment options, such as targeted therapies and immunotherapies, are also being explored in both human and veterinary medicine. Unfortunately, there are no cancer immunotherapies licensed for veterinary use, however research data are promising.

A range of clinical trials in canine lymphoma are recruiting patients (predominantly in the USA), and details can be found here. As of June 2023, there are a couple of clinical trials actively recruiting canine lymphoma patients in some parts of Australia, and patients may be referred by their veterinarians, with details available here and here. If you wish to find out more for your loved one, please discuss options with your veterinarian.

I dread the days when an older large or giant breed dog comes to the clinic with pain or lameness, usually in a single front leg. In many cases, the diagnosis is terrible: osteosarcoma (OSA), or bone cancer, a brutally painful and aggressive cancer that has metastasised to the lungs in 90-95% of dogs when they first show signs of swelling, lameness, and pain. 

The cancer is relatively common in dogs, with over 10,000 cases diagnosed in the USA, per annum. This is likely an underestimate.

Dr Bec Vet's dog Hilda, the Irish Wolfhound 
There appears to be a genetic predisposition to OSA, as it predominantly affects Boxers, Irish Wolfhounds, Greyhounds, St. Bernards, Dobermanns, Rottweilers, German Shepherds, Great Danes, Golden Retrievers and Irish Setters. Gentle giants are overrepresented, with most cases occurring in dogs over 40kg.

The cancer usually develops in the radius and ulna (above the wrist) or tibia and fibula (below the stifle or knee). Affected dogs may be painful, lame, lethargic, off their food, and may develop a dry cough. Other areas of the body can be affected, such as the toes, hip, or large bone of the hind leg (femur) but this is less common. Rarely, OSA can arise in the jaw, ribs, or other parts of the body.

The prognosis is terrible: dogs usually require amputation, and palliative care, such as strong pain relief and radiation therapy; most survive less than a year, usually only a handful of months. Only 25% of dogs survive more than 2 years, and these cases involve aggressive surgical, radiation and chemotherapy interventions. Eighty percent (80%) of dogs with OSA die due to the secondary tumours in the lungs.

Although these statistics are grim, it’s not all bad news. There are numerous clinical trials studying new ways to diagnose OSA earlier, before it metastasises, and investigating new therapies. A silver lining in this dreadful disease is that such studies directly help humans with the same condition.

Although very rare, affecting fewer than 1000 humans in the USA each year, osteosarcoma does develop in people, and almost always in children. OSA in dogs and children is nearly identical, and advances made in dogs have helped and are continuing to help kids. The ‘limb sparing’ surgeries, meaning a child can avoid amputation, were developed in none other than our wonderful canine friends with the very same disease.

A 2020 study identified common gene mutations in Irish Wolfhounds and Rottweilers, linked to developing OSA. Studies like this may help develop tests for earlier diagnosis of the disease in both dogs and people and provide new targets for cancer treatments.

Dogs may be enrolled in clinical trials for new therapies and these trials only offer potentially lifesaving new treatments for dogs with OSA and provide invaluable data on the safety and effectiveness of these treatments, which accelerates the process of making these treatments available for humans. Unlike many studies involving laboratory rodents, therapies that work in dogs with OSA are very likely to work in people.

In North America alone, over 80 clinical trials have studied new interventions for OSA, and 13 are currently recruiting. One fascinating study is investigating the link between dysbiosis, or an unbalanced gut microbiome, and OSA in dogs. We know that intestinal dysbiosis is associated with certain cancers in humans, and also whether or not patients will respond well to therapy. Perhaps the same applies in dogs. Again, if we find a link in our pets, we may have a new target for therapy, or option for intervention, to allow for earlier diagnosis and a better prognosis.

The University of Minnesota is recruiting healthy Irish Wolfhounds, and other large breeds, for a study to see if a simple blood test can detect OSA. This is funded by the Irish Wolfhound Foundation, however, at this stage, only dogs living in the USA can be enrolled. Up to 20% of Wolfhounds will develop this heartbreaking illness.

If you have a Golden Retriever, Dane, Irish Setter, Wolfhound, Rotti or Leonberger and live in the USA, please contact the group here. For canine osteosarcoma, there are no active trials in Australia.

Bladder cancer in dogs shares many traits with bladder cancer in humans. This is a rarer cancer in dogs, though one we must be mindful of, and signs of this cancer include difficulty and pain when urinating, accidents in the house, blood in the urine, and persistent or recurring urinary tract infections. There are some fascinating USA trials looking at the effects of adding probiotics, or orally administered ‘beneficial bacteria’ to standard treatments.

There is a genetic predisposition to bladder cancer, with Scottish terriers, West Highland White Terriers, Beagles, Australian Shepherds, Cattle Dogs, Jack Russell and Fox terriers and Bichon Frise breeds most commonly affected. 

A urine test that detects a common genetic mutation (a BRAF test) can be used to diagnose bladder cancer in many cases, though the urine sample must be sent to the USA for testing.

Amazingly, humans and dogs are the only species that spontaneously develop primary brain tumours. 

In dogs, around 35% of brain tumours are ‘gliomas’. 

Even with aggressive treatment, the prognosis for both dogs and humans with gliomas is terrible, and there are no cures. Shorter-faced (or brachycephalic) dogs such as English and French bulldogs, and Boxers, are more commonly affected than other breeds.

Currently, we use surgery, chemotherapy, and radiation to extend lifespan and improve quality of life in both our pets and us. 

A trial in Virginia, Maryland, is investigating the use of specially-targeted chemotherapy drugs, delivered directly to a dog’s brain tumour. The Johns Hopkins Hospital is trialling a novel chemotherapy agent in canine brain tumours, and it is hoped that this will also help humans. 

It is hoped that this new drug will target numerous types of cancer, and unlike many current chemotherapy drugs, this one can travel across the blood-brain barrier into the brain, and gain access to tumours. Data is promising in mice with brain tumours, and the drug is now being tested in pet dogs with gliomas.

Likewise, the dog is the one of the only species, apart from humans, to develop prostate cancer. Treatments are being co-developed in both dogs with this cancer, and humans.

Another breakthrough that may help people came with the development of a vaccine for melanoma in dogs. Canine melanoma, especially oral melanoma, is highly aggressive and usually resistant to standard therapies. The vaccine, developed initially for dogs, has paved the way for similar immunotherapy strategies in humans with melanoma.

Scottish Terriers have an increased risk of
Transitional Cell Carcinoma
Advances in genetics, including the Canine Cancer Genome Project, through the Animal Cancer Foundation, aim to map the genes or DNA of cancers affecting different dog breeds, and may lead to better treatments for both dogs and humans. 

Therapies may be tailored to the DNA of an individual pet's tumour, which is the same as ‘precision medicine’ in humans. This is not yet available in Australia, though is being used to make smarter treatment decisions for pet patients in the USA.

Our dogs, and to a smaller degree, cats, are helping us understand the biology and treatment of both human and companion animal cancers. The remarkable similarities mean studying cancer in our pets can provide important information that fast tracks drugs to the clinic for both veterinary and human medicine. 

Given their shorter lifespans, trials in our pets give us rapid insights: a drug that extends the life of a dog for 1 year may extend that of a person for 7, or longer. There is great hope for all of us affected by cancer … with the cure right by our side.

written by Dr Bec, October 2023 for Australian Dog Lover (all rights reserved).

About our writer

Dr Rebbecca Wilcox (Dr Bec) is a Melbourne-based veterinarian and academic, working in the clinic, animal welfare, the media and medical research. She has a passion for sharing fascinating facts and the latest research on the intriguing lives and science of all animals, particularly those we share our lives with.

Dr Bec is a regular guest on Melbourne radio, a columnist for Australian Dog Lover MagazineAustralian Cat Lover Magazine, and Pet Insurance Australia, and she presents short segments on all things animal related (see Insta and Facebook). Her emphasis is on sharing of evidence-based veterinary advances and the empowerment of pet parents, and society, through promoting medical literacy, or the understanding of our pets’ health, and our own. She relishes reaching out to all animal loving audiences.

Her academic and clinical research spans several areas, with a focus on the role of the microbiome in pet health, preventative medicine, developing new veterinary medicines, clinical trials that benefit animals and humans, and working to prevent antibiotic resistance.

Dr Bec advocates for animal charities that promote animal welfare, in Australia and overseas.
Her blog can be found at: and she may be contacted at

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