There are many similarities between man and dog, and one of them – unfortunately – is cancer. Cancer is currently the leading cause of death among domestic dogs, and the cancer varieties they can develop are closely related to the cancers we see in humans.

Statistics show that one in every three dogs will develop cancer at some point during their lifetime; most dogs will get cancer at a later stage, but it may also affect dogs that are still young. Some dog breeds are more prone to cancer than others, but no dog is immune to this tragic disease.

Luckily, there is treatment available if the cancer is discovered in time, and many dogs make a full recovery, but there are also those that don’t. It is a difficult subject that few are willing to think about but learning what canine cancer is can help if it would happen to your dog.

Different Types of Cancer

The cancers found in canines are often the same as those found in humans; the same terminology is used, and the treatments administered are also similar. In dogs, skin cancer is usually caused by mast cell tumors, and this cancer affects a blood cell that plays an important part in the way the canine body handles inflammation and allergens.

This skin tumor is the one most commonly found in dogs and it can also affect other areas like the liver, bone marrow, the gastrointestinal tract, and the spleen.

Dogs can also get prostate cancer, brain cancer, and lymphoma. These are scary words that you may associate more with humans, but a dog can also be diagnosed with these conditions. The type of cancer the dog has will determine the course of treatment, and how far along they are will decide whether cancer can be treated, or if it is time to start preparing for the end.

Dogs are also one of the three species (currently known) that can contract something called CTVT – Canine Transmissible Venereal Tumor. Unlike other cancers, this is a variety that is highly contagious, and that one dog can pass onto another.

A tumor-like this can be contracted by another canine through close physical contact; when dogs mate (intercourse), or if a dog licks, sniffs, bites or scratches a dog that is already infected – especially if they come in contact directly with an exposed tumor.

CTVT is very common in areas with large stray dog populations, as many of them go through the course of the disease without treatment.

CTVT is initially close to invisible, and the first few signs could be something as subtle as bloody urine. As time goes by, however, a tumor starts growing in the area of the dog’s genitals; the tumor can easily burst or get infected and spotting a stray dog with advanced CTVT can be a gruesome sight.

It can be treated and cured provided the dog is brought to a veterinarian, and it is one of the more visually unpleasant cancer forms in dogs. The good news is that CTVT is not contagious for humans, so fear should not prevent us from bringing an infected dog the veterinary attention they so desperately need.

Hemangiosarcoma is another cancer type you might not have heard of, and the reason for this is that it is almost only the dog that is known to be at risk for it. There have been a few documented cases in horses and cats, but dogs are the primary host when this disease strikes. This cancer consists of the formation of small tumors on the blood vessels, and they can pop up anywhere on or even inside the body.

Hemangiosarcoma is known to occasionally attack the blood vessels inside the inner organs, making them difficult to spot without a thorough examination by a veterinarian. They are malignant and can go on to killing your dog, usually when rupturing – resulting in extreme blood loss.

What Causes Canine Cancer?

Sick dog

There is no point in sugar coating canine cancer, because if this disease ends up affecting your dog – you need to be ready for it. Dogs are incredibly resilient, and a diagnose is not necessarily a death sentence. So, why do dogs get cancer? There is no easy way to answer such a complicated question; because cancer is a very complex disease with many factors playing a role in its existence.

DNA mutations, dysfunctional proteins, aberrant cell cycle regulations, and chromosomal translocations have long been linked with carcinogenesis; the cell DNA is altered by cancer and neoplasms occur due to the daughter cells receiving mutated genetic material.

Does this sound complicated? It is, and it is the information most of us are unable to fully comprehend (or even begin to comprehend), so let’s leave the complicated terms behind and look at what may set off these reactions in the canine body. Canine cancer can be hereditary, but it can also be caused (or worsened) by exterior occurrences.

Some of the known carcinogens – things that cause cancer in pets – are similar if not the same as what is known to cause cancer in humans. Dogs live and grow up in the same environment as we do, so it should not come as a surprise that their bodies are affected similarly.

Long-term exposure to sun and the ultraviolet radiation found in sunlight is known to increase the risks of canine cancer, along with second-hand cigarette smoke. You might not want to hear this, but by smoking at home or when out walking with your dog – you may be contributing to future cancer diagnose for your dog (and possibly also for yourself).

Insecticides and pesticides – the kinds used frequently in agriculture – are also risk factors that may cause cancer if your dog is exposed long-term; along with smog and air pollution in bigger and more populated cities. Other known carcinogens are (but are not limited to) asbestos, vinyl chloride, benzene, cadmium, nickel, uranium, and benzidine.

It is impossible to say which ones are more dangerous and which will have a greater effect on your dog, as all dogs are different, and some might be more resistant to carcinogens than others. If your dog does get cancer, it is unlikely that anyone will be able to tell you the exact reason it happened (except for in the case with CTVT, where the “how” is easier to establish), and it matters little for the treatment plan.

Dog Breeds Prone to Cancer

German Shepperd

Research has shown that some specific dog breeds seem a lot more likely to get cancer at some point during their lifetime, especially when compared to certain other breeds. This indicates that there are hereditary risk factors potentially deciding which dogs get cancer and which do not, and not just environmental causes such as cigarette smoke.

Golden Retrievers, Bernese Mountain Dogs, and Boxers are three breeds that are frequently mentioned as breeds more likely to get cancer, but the following dogs are also considered higher-risk breeds:

+ German Shepherd
+ Bouvier des Flandres
+ Boxer
+ Labrador Retriever
+ Bernese Mountain Dog
+ Rottweiler
+ Golden Retriever
+ Great Dane
+ Bichon Frise

If you own one of these dog breeds, it does not automatically mean that your beloved fur friend will get cancer, and it also doesn’t mean that dogs of any other breed (or mixed breeds) are safe. All dogs, regardless of breed and size, are unfortunately at risk of getting cancer, just like us humans.

Cancer Symptoms in Dogs

Cancer presents itself in very different ways depending on the dog, and sometimes there could be almost no symptoms at all until it is already too late. Whenever you notice something different about your pet; a change in behavior or a lump that wasn’t there before – talk to your veterinarian to see what can be done.

An early diagnose can be what saves your dog’s life, and it is always better to take your dog to the vet (even if you are told you worried for nothing) than to not take your dog to the vet and find out you could have saved him if you had gone in time. A few possible symptoms of canine cancer are:

+ Loss of appetite
+ Bad breath
+ Swelling
+ Lumps
+ Lethargy
+ Unusually dark stools
+ Sudden weight loss
+ Abnormal discharge
+ A strange and unpleasant odor
+ Difficulty breathing
+ Difficulty urinating

All these symptoms could also be the symptoms of something else, or of nothing, so just because your dog refuses to eat one day it doesn’t necessarily mean it has cancer or any other serious illness. If strange symptoms persist and/or if you are worried – make a call to your trusted veterinarian to see what he or she recommends.

What We Know About Canine Cancer

There are documented cases of cancer in humans dating back over 2 000 years, which shows that doctors and physicians were aware of the existence of this disease already back then. Canine cancer is less explored, and veterinarians and experts are only just beginning to dig into the research required to fully understand how it potentially differentiates from cancer in humans, and what the true causes are.

What is known so far is that cancer seems to be more frequently occurring in older animals than in those that are young, and a theory is that the immune system might become weaker as a dog age – making it significantly easier for regular cells to start mutating into initiated- and precancerous cells. This would explain why the cancer rate seems to be much higher in animals over a certain age, but researchers are most likely only just starting to scrape the surface of this issue.

Available Treatments

Canine cancer is treatable, bur, whether recovery is a possibility, depends on how far along your dog is by the time the disease is discovered. Surgery, radiation, and chemotherapy are some of the treatments used to try to remove growing tumors and to “kick cancer out” of your dog’s body; which option is used depends on the type of cancer, how advanced it is and what the particular veterinary clinic is able to offer, and there are never any guarantees for a full recovery.

The veterinarian might recommend one specific treatment or a combination of several treatments, and for us dog owners we will simply have to trust that they are giving our dogs a fair chance to live. When opting for surgery, the tumor is physically removed, and this is common both for very large tumors but also for smaller ones. It is sometimes followed up with radiation, with chemotherapy or with both depending on how successful the operation is.

Chemotherapy is an umbrella term for a variety of medical treatments for cancer; it is sometimes injected (sometimes directly into the tumor), it can be taken orally, as a topical treatment and more, and your veterinarian will decide what has the best chances of helping your dog with his/her specific condition.

The side effects for pets receiving chemotherapy are relatively few; they don’t lose their hair the way humans do (even though dogs with a specific hair type may experience a thinner coat than usual, in rare cases), and what you can expect to see is lethargy and sometimes vomiting after treatment.

Costs for Treating Canine Cancer

How much it would cost to try and save your dog from cancer is something only your veterinarian can answer. The cost varies greatly depending on the type of cancer, how far along your dog is, the treatment that will be required (keep in mind that several treatments are usually needed), the prices set by your veterinarian, whether your dog will need continuous care after potentially being cured and more, so the only way to answer this question is to keep an open dialogue with the veterinarian of your choice.


Cancer is an incredibly complex subject, both in humans and dogs, and it would take a 400-page book to even begin to explain it. This guide is meant to be an introduction to a disease many dogs and owners will, unfortunately, be diagnosed within their lifetime, and your veterinarian will give you more specific information regarding your dog’s medical condition and/or health state. If you have concerns – always reach out to a licensed vet, especially if your dog is presenting persistent symptoms or signs of unusual behaviors.

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Janni is a dog loving writer who currently shares her home with two rescue dogs - Emmett and Frankie. Writing doggie-inspired articles is a way for Janni to share her knowledge, find inspiration, and help others.