Everything You Need To Know About Dog Cancer

Picture of a dog outside

Cancer affects our canine friends in almost the same way that it affects us — it steals some years from their lives and their quality of life, too. Veterinary research has evolved a lot through time, and it continues to improve all dog’s possibilities to live a long and happy life.

Here is almost everything you should know about canine cancer – from its causes, common types, and signs, to what treatment options are available nowadays, whether you can prevent this disease, and what an anti-cancer diet is.


Cancer isn’t considered a new disease as medical professionals have been aware of it for over 2,000 years. It’s true that most of the progress was made in the area of understanding the development and spread of cancer in humans, so vets know a little less about the actual specifics of it in animals.

Age is an important potential factor when it comes to cancer as many vets and pet owners have noticed that pets develop this disease more frequently in the late stages of their lives. However, there are a variety of additional factors, some of which make perfect sense and others that are merely suspected.

Family History and Genetic Factors

There are some breeds that are more predisposed to developing cancer during their lifetime and these are Golden Retrievers, Bernese Mountain Dogs, as well as Boxers. There is a lot of research done on this topic and it has shown that there are genetic characteristics which contribute to significantly higher rates of cancer among these particular animals.

The increased risk that they face could be caused by a single gene, but it could also be caused by a combination of several.

Carcinogens, Viruses, and Other Causes

Veterinary researchers have found that some cancers actually have specific causes. The majority of animal species develop squamous cell carcinoma and it is suspected that it is a result of prolonged exposure to ultraviolet light. Therefore, exposure to sunlight is a risk factor (and as you probably know, it is for humans, as well).

Oral papilloma is caused by a virus, and some types of cancers are transmitted sexually. Dogs have a transmissible venereal tumor which is passed on from a carrier to another dog during intercourse. The cancerous cells are transferred when a healthy animal gets in contact with an infected animal.

It is also believed that chronic inflammation (such as the one that results from short-lived physical injuries such as bruises or bumps or that resulting from bone fractures or the sites of implants) increases the risk for the animal to develop sarcomas. Sarcomas can also develop at vaccination sites, which is something that vets have started noticing in the early 1990s.


Both in humans and in animals, cancer is a disease that occurs more frequently in older adults. It makes sense, after all, as aging weakens the individual’s immune system, which means that the body’s ability to control mutated cells is less effective. As healthy cells reproduce and divide continuously, vet cancer specialists speculate that as a dog becomes older, the chances of a cell dividing incorrectly and producing an error leading to mutation are higher.

Furthermore, the longer an animal lives, the longer they are exposed to various environmental factors (one of them being cigarette smoke, for example, which causes oral squamous cell carcinomas in cats). The majority of the cases that I personally analyzed while doing my Ph.D. thesis were from dogs that were older than the age of 8. Therefore, it is not incorrect to assume that there is a direct correlation between the pet’s age and the development of cancer.

Environmental Factors

Some risk factors can be found in the environment, but others are part of a dog’s diet. Some of the well-known carcinogens that could contribute to the development of the disease in pets range from long exposure to the sun and ultraviolet radiation to a variety of insecticides, pesticides, or herbicides used in agriculture. Second-hand tobacco smoke is another factor that we’ve already mentioned, but there are others such as smog or air pollution.

Dogs that live in urban areas have a higher likelihood of developing cancer than those that live in the country. However, the latter are exposed to the chemicals that we have mentioned, so they aren’t in the clear either. And finally, there are some substances that have been identified as carcinogens, and these are:

  • Uranium
  • Nickel
  • Benzene
  • Benzidine
  • Vinyl chloride
  • Cadmium
  • Radon
  • Asbestos

Common types of Cancers in Dogs

Dogs are susceptible to most types of cancer that affect humans, too. In fact, canine cancer has been the leading cause of death for dogs older than the age of 10 for several years now. While half of the cases of cancer are treatable, this largely depends on the type of tumor, but also on whether or not it is diagnosed in the early stages.

Some of the most common types of cancer in dogs are the following.

Mast cell tumors

These cells are responsible for allergies. They can be found in all body tissues, but the tumors that they form are usually present on the skin, and they occur in approximately 20% of the whole canine population. They can be benign but also very aggressive. Some breeds are at a higher risk of developing this type of cancer, which means that genetics can be one of the predisposing factors. Boxers have been found to be particularly prone to getting this tumor.


This is a type of incurable tumor of the cells that line blood vessels (endothelial cells). This kind of cancer usually occurs in middle-aged to senior dogs, but it can affect almost any age and breed. Some breeds were found to have a significantly higher incidence, and they are German Shepherds and Golden Retrievers. It is, therefore, a good idea to perform screening on these dog breeds beginning with the age of 5.

Because hemangiosarcoma takes some time to develop, and it does so in a painless manner, the clinical signs are not obvious until an advanced stage of the disease has been reached. Unfortunately, less than half of the dogs that receive treatment for this type of cancer survive for more than 6 months. Many will die because of internal bleeding before there’s any chance of a veterinarian initiating treatment.


This type of canine cancer affects any dog, regardless of age or breed. Clinically, it usually appears as inflamed glands (meaning the lymph nodes). These swollen areas can be noticed or felt in front of the shoulders, under the neck, or behind the knee. However, there are lymph nodes inside the body, too, and those aren’t visible to the naked eye, which means that dogs could suffer inflammation in the abdomen or inside their chests. Some of the breeds that have a higher incidence of this cancer are Golden Retrievers, Standard Poodles, as well as Australian Shepherds.

Brain tumors

Brain tumors are somewhat rarer compared to some of the other types of cancer that we have showcased here. Two typical clinical signs that could indicate their presence are extreme behavioral changes or epileptic-like seizures. MRI and CAT scanning are utilized to determine the size of the tumors, their severity, and also their exact location. While inoperable tumors can be partially controlled thanks to radiation therapy and oral chemotherapy, surgery might be the right way of going about things if the tumor can be removed safely.


As one of the most common types of primary bone cancer in our furry friends, osteosarcoma makes up for about 85% of all tumors which originate in the skeletal system. It is known to affect older giant or large breed dogs, but it can also show up in smaller breeds and younger patients. It can occur in any area of the body, but it typically affects the bones that border the shoulder, knee, and wrist. Swelling in the area or lameness in the affected leg are present clinically.

Mammary carcinoma

Around half of all mammary tumors are malignant, which is why complete surgical removal is advised if the cancer hasn’t had the chance to metastasize. This type of tumor occurs in females that haven’t been spayed, but it can also affect female dogs regardless of age or reproductive state.

Bladder cancer

This type of cancer takes between three and six months to fully develop, and that’s why pet owners have the opportunity to notice its clinical symptoms, which usually consist of bleeding and urinary obstruction. According to akc.org, some of the breeds that are predisposed to bladder cancer are Shelties, Beagles, West Highland White Terriers, Scottish Terriers, and American Eskimo dogs.


This type of cancer commonly affects dog breeds that have dark skin. Melanomas are caused by a mutation of melanocytes, which are cells that are responsible for giving the skin its color. Melanomas can occur in areas with hair, where they form dark and small lumps, but they can also show up as wrinkled and large masses. Malignant melanoma usually develops in the distal limbs and in the dog’s mouth, and it is incurable. If the tumors get to spread to other parts of the body, they are often impossible to remove surgically.

Mouth and nose cancer

This is a somewhat common type of cancer, and it affects the mouth more than it does the nose. Some of the symptoms that are noticeable range from the actual presence of a mass on the gums to odor, bleeding, and difficulty eating. Nose cancer is characterized by difficulty breathing, facial swelling, or bleeding from the nose.

Squamous cell carcinoma

Compared to other kinds of cancer, this one is usually found in the nail beds of the toes or in the mouth. Fortunately, less than 20% of the dogs that are diagnosed with squamous cell carcinoma ever develop metastatic disease. However, if the tonsil or the tongue have been affected, SCC can be very aggressive, with less than 10% of the dogs surviving 1 year or longer in spite of any treatment.

Malignant histiocytosis

Large sport breeds are at a higher risk of developing this type of cancer. It occurs as localized lesions on the lung, skin, brain, lymph nodes, and spleen. Histiocytic sarcomas can be found to have affected a single organ in multiple areas, thereby causing multiple lesions — they typically disseminate fast and affect other organs. At the time this article was written, there wasn’t any effective therapy for this particular form.

Testicular cancer

Testicular cancer usually appears in dogs that weren’t neutered. Neutering largely prevents this disease and when it is diagnosed in due time, the treatment can be very effective.


Given the many types of cancer that affect dogs and the fact that they often occur in different organs, there is no specific set of general symptoms that you can notice for all types. However, even if the signs can vary significantly depending on an array of factors, you should be able to see the following symptoms:

  • Lethargy
  • Depression
  • Lumps and bumps underneath your pet’s skin
  • Abnormal discharge from the mouth, eyes, ears, or rectum
  • Abnormal odors from the ears, mouth, or other body parts
  • Abnormal swelling
  • Sudden weight loss
  • Difficulty breathing or coughing
  • Changes in appetite
  • Changes in bathroom habits
  • Non-healing sores or wounds
  • Pain


A variety of tests are available nowadays and they can say for sure whether a dog suffers from cancer or not. However, before we move on to mention them, we’d like to note that screening is particularly important if you are the pet parent of a dog breed that is known to be genetically predisposed to one form of cancer or the other. That’s why it is highly recommended that you take your canine friend to the vet once or twice a year for some bloodwork and a general physical exam.

If the veterinarian suspects that a dog has cancer, he or she will most likely recommend a full set of analyses, an X-ray (or several), an ultrasound exam, and in some cases, even a CAT scan or MRI. Once these are performed, a biopsy is usually necessary to determine the exact type of tumor, its grade, and whether it can be removed surgically or not. Many benign tumors can be removed surgically, but with malignant ones, it’s a little more complicated in that they might have already spread to other organs, which often makes an operation impossible.

Picture of a Golden Retriever getting an operation

Treatment Options

Three major types of treatment are available. Surgery is one of the most commonly used therapies, especially in the types of cancers that are benign. Then, there’s chemotherapy, which consists of administering medication to the canine patient so as to ‘kill’ the cancerous cells. Radiation therapy is extremely effective, as well, but it does present some risks and it is likely to cause pain in some patients.

Choosing one type of treatment over the other needs to be done after the dog parent has had a long and detailed conversation with the vet. Some of the factors that influence treatment decisions are the dog’s age, their general health, the type of tumor, its biological behavior, and the stage of the cancer. In many situations, combination therapy is usually the most effective. For example, a dog can receive chemotherapy before or after the surgery.

These days, stem cell transplants are available for dogs that have been diagnosed with blood cancers, and they are typically very effective. Another type of treatment is immunotherapy, which comes in the form of an anti-cancer vaccination that has the role of strengthening the immune system against the invading tumor cells.

Holistic or herbal therapy can also be a choice, especially for inoperable cases.


As you might have noticed from the section where we discussed the causes of cancer in dogs, it’s very difficult to say just how you can prevent this particular disease. If you are the owner of a dog breed that’s likely to develop cancer throughout their life, screening is the best way of preventing it. There are cases (many of which I’ve seen) where some dog parents will wait for months and even years after they’ve noticed a lump or a bump underneath their canine friend’s skin before they take their companion to the vet.

Since cancer treatment can be very expensive, we urge you to get pet insurance so that the costs don’t make it impossible for you to give your canine companion the chance to live a long and happy life.


As much of a common disease as it is, there are still many myths about cancer. Around 50% of all dogs and 30% of all cats are affected by a tumor during their lifetimes, and a recent report has shown that about 50% of dogs that are older than 10 are going to die from cancer. Let’s look at some myths about cancer, which are, unfortunately, untrue, and also very common.

1. Cancer is more common today than it used to be in the past

In a way, yes, but in another, also no. Pets have access to excellent healthcare nowadays and as such, they get to live longer lives. Back in the day, it used to be that most dogs only lived to get to 12 years of age, for instance, and that happened only in the happiest of cases. Circumstances where dogs got to live to be 18 to 20 years old were extremely uncommon — but nowadays, that’s not an impossible dream.

We’ve already explained the correlation between aging and the occurrence and development of cancer, so the total number of cases that are diagnosed is naturally higher because dogs get to live for a longer amount of time.

2. Cancer treatment is just a way of delaying the inevitable

There are several types of treatment and as you might know, not all types of tumors are the same – some are benign whereas some are malignant. Even in some cases where the cancer is aggressively malignant but discovered in time, your dog can have a very good chance of leading a long and happy life following surgery, radiation, or chemotherapy.

In cancer, treatment is targeted to giving the animal patient a good to great quality of life for a significantly longer time than it would otherwise be possible. In a nutshell, treatment is often used to extend your pet’s life and allow him or her to be at your side for a while longer.

3. Waiting doesn’t do more harm than good

Waiting to treat cancer can be a choice when it comes to benign tumors. However, with aggressive and malignant cancers, it is most definitely the wrong way of going about things. As a tumor becomes larger and occupies more space and even endangers other organs, its treatment will require more money and more effort on your behalf and on your pet’s behalf, too. The patient will effectively become sicker so as such, he or she might experience more side effects.

It is always a good idea to avoid waiting simply because a dog with a healthy immune system (or one that’s in good shape) has the physical ability to withstand the aggression of treatment (such as radiation or chemotherapy) a lot better than a debilitated animal ever could.

4. A biopsy isn’t necessary

Actually, a biopsy or a needle aspirate is the only way you can find out a correct and specific diagnosis. We, vets, can’t say whether a tumor is benign or malignant or in which malignancy stage it might be simply by looking at it. Sure, we might be able to make a difference between a lipoma and something else, but we don’t know any other details.

The biopsy is an amazingly specific test as it can also reveal the grade of the tumor and whether its margins are clean. If you are considering surgery as a treatment option, a biopsy is something that the dog needs. It is not a choice – it’s required.

5. Chemotherapy can make a dog with cancer even more sick than he is

While vets do use many of the same drugs which are used in human oncology, they are extremely careful and they use them at much lower doses. Vets do not give patients as many drugs by comparison to human medicine oncologists as they want to minimize the risk and severity of the side effects.

Everyone knows that chemotherapy comes with a share of side effects, but just about 5% of all patients suffer reactions that are actually serious enough to call for hospitalization. It is estimated that less than one quarter of all patients actually suffer any side effects whatsoever. Chemotherapy-associated fatality happens in less than 1 in 200 cases. In case toxicity is noticed, the drugs can be replaced with others or lower doses can always be utilized.

Anti-cancer diet

Feeding a dog that has cancer can be very challenging. First things first – talk to your vet and find out what options you have at your disposal. It is, however, generally acknowledged that dogs that have this disease aren’t supposed to eat a lot of carbs as they cause a net energy loss to the patient, but can be readily used by cancer cells.

Also, it’s a good idea to use fish oil supplements (containing Omega 3 acids) as they are known to reduce or even eliminate several of cancer’s metabolic alterations. Since weight loss and anorexia have a severe negative impact on a dog’s general wellbeing and they can effectively speed his or her death, you should find the most appetizing (yet healthy) food that you can get.

Organic foods with ingredients that are fresh, easily digested, palatable, and bioavailable are highly recommended. Vitamin C is known for its antioxidant properties, and high-quality meat is both appetizing, but also bioavailable. Fresh veggies have the purpose of providing the essential nutrients to the dog so that they maintain normal bowel health. You can also use digestive enzymes and garlic, as the latter is known to contain inhibitors that slow down the cancer process.



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