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A Comprehensive Guide to Dog Cancer

Why Do Dogs Get Cancer?

Dog at the Vet

The word "cancer" can get people's attention. It's one of the most feared words in our language, and for good reason — when someone has cancer, they have a serious health problem that can be life-threatening. Cancer is not just a human problem, it also affects animals!

And while it affects all types of animals, dogs are particularly susceptible to the disease. Dogs have a lifetime risk of developing cancer that is almost identical to that of humans - about 1 in 3 for both species. Dogs develop cancer at approximately the same rate as humans. In fact, cancer is the leading cause of death in dogs more than 2 years old. Cancer is the leading cause of death in dogs over the age of 10, and 50% of dogs over the age of 10 will develop cancer.

Dogs get many of the same types of cancers that humans do, including leukaemia and lymphoma, breast cancer and osteosarcoma (bone cancer). The most common types are skin cancer, lymphoma and mast cell tumours.

There are a number of theories about why our canine friends are so vulnerable to the disease. First, some breeds have a higher risk of certain cancers. For example, Boston terriers have a high rate of mast cell tumours and German shepherds are at increased risk for hemangiosarcoma (a type of tumour that arises in blood vessels).

Another theory is that dogs live in such close proximity to us that they're exposed to many of the same risks as humans — such as pollution and pesticides — but because their life spans are much shorter than ours, they develop symptoms sooner. The result: Dogs can serve as an early warning system for illnesses like cancer, which may also affect people if we're exposed long enough.

Symptoms of Cancer

According to the American Veterinary Medical Association, about half of dogs over the age of 10 will develop cancer. Without good care, most dogs die within a year of being diagnosed with cancer.

It's not just older dogs that get sick, though. Puppies and younger dogs can develop cancer as well. In fact, osteosarcoma — a type of bone cancer — is most likely to affect large and giant breed puppies, according to the American Kennel Club (AKC).

It's important to know that even though it seems like your dog has all the symptoms of a serious disease, it could be something else. That's why it's important to take your dog to the vet if you notice any changes in his behaviour or appearance.

Dogs, like their human counterparts, may develop cancer at any time in their lives. The more we learn about this disease, the more we are able to help our furry friends live longer and healthier lives.

When considering your pet's health and well-being, there are a number of factors to consider. The most important is that you are aware of the signs and symptoms of cancer in dogs.

Most cancers are not painful in their early stages, but can be detected by a veterinarian during an exam with a blood test or imaging (x-rays or ultrasound). Some tumours will also cause pain later on as they grow larger.

Some signs of cancer in dogs are easy to spot and others are not. Signs of cancer in dogs may vary greatly depending upon several factors.

However, the following list identifies some of the most common signs of cancer in dogs:

  • Lumps and bumps underneath a dog's skin

  • Abnormal odours emanating from the mouth, ears, or any other part of the body

  • Abnormal discharge from the eyes, mouth, ears, or rectum

  • Abdominal swelling

  • Non-healing wounds or sores

  • Sudden and irreversible weight loss

  • Change in appetite

  • Coughing or difficulty breathing

  • Lethargy or depression

  • Changes in bathroom habits

  • Evidence of pain

    Should you witness any signs of cancer in your dog, we strongly recommend making a veterinary appointment immediately.

    Keeping a watchful eye for any symptoms is paramount to your dog’s health and longevity. Any suspicion requires an immediate call to your vet, even if out of an abundance of caution.

    Causes of Dog Cancer

    If you've found yourself wondering, "Why do dogs get cancer?" you're not alone. While cancer is not an inevitable part of aging, unfortunately it is very common in dogs. The causes of cancer in dogs can be difficult to pin down but breed, environment, gender and genetics are all important factors.

    Many different factors may contribute to the development of cancer in dogs, including: 

    • Genetics

    • Environmental agents (toxins/pollutants)

    • Infection with viruses or bacteria

    • Hormonal factors (such as reproductive hormones)

     However, most often the cause is unknown.

    Breeds with Higher Chance of Cancer

    Dogs tend to develop most cancers later in their lives, but some breeds are known to be at higher risk for specific types of cancers, like osteosarcoma, often at a younger age.

    A breed’s genetic vulnerability isn’t the only factor, however. Individual dogs of any breed have higher or lower sensitivities that may affect whether or not they develop cancer, and how that cancer behaves.

    Some dog breeds have a genetically higher risk of getting cancer than others these include:

    • Golden Retrievers

    • Boxers

    • Bernese Mountain Dogs

    • Rottweilers

    Is Dog Cancer Preventable

    The good news is, there are several things you can do to help prevent dog cancer. For some cancers, there are steps you can take to lower the risk of your dog getting cancer. For example, its known that sun exposure contributes to skin cancer in dogs, so keeping your dog in the shade or using a sunscreen on his exposed areas can help protect him from this type of cancer.

    It’s also been established that spaying and neutering can reduce the risk of certain types of reproductive cancers, which is why it’s recommend all dogs be altered by six months of age. That said, even if you did everything perfectly, some dogs would still get cancer.

    On a day-to-day level, the most important thing you can do to help keep your dog fit, healthy, and cancer-free for as long as possible is to manage their weight.

    According to veterinary nutritionist Dr Lisa Weeth  “There’s some potential correlation between being overweight and certain types of cancers in dogs. Some benign types of tumours that dogs get, like lipomas, can occur more frequently in dogs that are overweight.”

    Earlier research, she adds, suggested that overweight dogs, especially female dogs, may be at an increased risk for developing mammary tumours. Additionally, obesity can increase the risk of joint disease and complicate things like diabetes and heart disease.

    For older dogs, certain dietary tweaks may improve their chances of remaining cancer-free. Antioxidants, like EPA and DHA (found in fish oils), and medium-chain triglycerides, have been found to improve cognitive function by helping to prevent damage to brain cells. They might also help prevent damage to other cells in the body.

    Since cancer is caused by damaged cells replicating unchecked, supplementing with these items may help protect against the development of some of the DNA damage that can lead to cancer.

    Studies show that antioxidant regimes don’t have the same impact on younger dogs as in older ones. So, from an efficacy perspective, this supplementation is best kept for the more mature canine.

    There’s also evidence that some environmental factors are associated with higher cancer rates in dogs. Some of these reflect similar information as what we know about cancer risks in humans.

    For instance, did you know that living in a smoking household is bad for your pets as well as humans? A study from Colorado State University has shown that second-hand smoke is linked to an increased risk of nasal cancer in dogs, especially long-nosed dogs like Labrador Retrievers, Collies, and Dachshunds. Meanwhile, short-nosed dogs like Pugs, Bulldogs, and Shih Tzus are more likely to develop lung cancer from living with a smoker. Lastly, all dogs are at risk of respiratory disease from second-hand smoke.

    Sunlight is also a risk factor, especially if you have a dog with light pigmentation. Keep such dogs out of the sun during the hottest hours of the day and use sunscreen when sunlight is unavoidable. Make sure to avoid zinc oxide, which is toxic to dogs if ingested.

    Types of Cancer

    Tumours that originate from within the body are called primary tumours while those that originate elsewhere but spread to other parts of the body are called metastatic tumours. Metastasis occurs when cancer cells move through the bloodstream or lymphatic system and form tumours in other parts of the body.

    Small clusters of cancer cells can break off from a primary tumour and spread to different parts of the body where they continue to grow and form additional tumours. These secondary tumours often have the same appearance as primary tumours, making them difficult

    The most common cancers in dogs are lymphoma, mast cell tumour, soft tissue sarcoma, and osteosarcoma (bone cancer).

    1. Lymphoma – Lymphoma accounts for 20% of all canine cancers, with dogs of any breed being 2-5 times more likely to develop lymphoma than humans. It often appears as swollen lymph nodes under the jaw, in front of the shoulders, or behind the knees. The swollen lymph nodes feel like firm lumps or masses under the skin but aren't typically painful when touched. These lymph nodes may also feel warm. When lymphoma attacks lymph nodes in the chest or abdomen, difficulty breathing, vomiting, and/or diarrhoea are often the prevailing symptoms.
    2. Mast Cell Tumours – These tumours typically form on the skin or under the skin and are considered “the great pretender” of canine tumours, as they can be mistaken as benign fatty lumps. Mast cell tumours are always malignant but can range in severity or grade. They tend to spread out quickly into the surrounding skin but typically do not cause the dog to be in pain until later stages. Dogs can develop more than one at a time on their body, so all masses should be examined. Mast cell tumours can also affect the internal organs such as the spleen and liver. They typically appear as a small, raised, hairless pink lump or soft squishy subcutaneous (under the skin) mass.
    3. Osteosarcoma – A common bone cancer in dogs, osteosarcoma most often affects large dog breeds and typically attacks long bones in the limbs, but it can also affect the skull. It rapidly spreads to the lungs, lymph nodes, and other bones, with pet owners noticing swelling, lameness, and limb pain first.
    4. Melanoma – The most common oral cancer in dogs, melanoma is most frequently found in breeds with dark tongues and gums. A malignant melanoma found in the oral cavity, which presents as a brown, black, or sometimes pink mass, has most often already spread throughout the body by the time it’s noticed. Dogs can also get melanoma on their toes which presents as a bulge or bleeding mass near the nailbed.
    5. Hemangiosarcoma – A form of canine cancer that develops from cells that line the blood vessels; hemangiosarcoma attacks the spleen, liver, heart, and skin. Early symptoms may include a soft or firm swelling under the skin, weight loss, bulging belly, lethargy, and decreased appetite. Symptoms can be delayed in presenting themselves until the tumour ruptures, when blood loss, sudden weakness, pale gums, and laboured breathing quickly presents in the dog.
    6. Brain Tumours: Epileptic-like seizures or other extreme behavioural changes are usually the only clinical signs. CAT scanning and MRI is used to determine location, size, and severity. Although some oral chemotherapy and radiation therapy can control some inoperable tumours, surgical intervention may be recommended if the tumour is operable.
    7. Bladder Cancer: Some breeds are more at risk for this form of dog cancer than others. This is a slow developing dog cancer, and symptoms may not show for 3 to 6 months. Urinary obstruction and bleeding are common symptoms.
    8. Mammary Carcinoma: Non-spayed female dogs are at high risk for developing malignant mammary tumours, but all female dogs regardless of reproductive state remain at risk. Approximately 50% of these tumours are malignant, and complete surgical removal is recommended if cancer has not metastasized.
    9. Malignant Histiocytosis: This dog cancer affects larger sport breeds most often. It occurs as localized lesions in the spleen, lymph nodes, lung, bone marrow, skin and subcutis, brain, and periarticular tissue of large appendicular (limb) joints. Histiocytic sarcomas can also occur as multiple lesions in single organs (especially the spleen), and rapidly disseminate to involve multiple organs. Unfortunately, there is no reported effective therapy for this form of dog cancer.
    10. Squamous Cell Carcinomas: It is most often found in the mouth and the nail beds of the toes. Early detection and complete surgical removal is the most common treatment. Fewer than 20% of dogs develop metastatic disease. SCC of the tonsil and tongue are quite aggressive and fewer than 10% of dogs survive 1 year or longer despite treatment measures.
    11. Mouth and Nose Cancer: This is a very common form of dog cancer, more so in the mouth than the nose. Symptoms include a mass on the gums, bleeding, odor, or difficulty eating. Since many swellings are malignant, early, aggressive treatment is essential. Cancer may also develop inside the nose of dogs. Bleeding from the nose, breathing difficulty, or facial swelling are symptoms that may indicate nose cancer.
    12. Testicular: This form of dog cancer is common in unneutered dogs with retained testes. This form of dog cancer is largely preventable with neutering, and curable with surgery if arrested early in the disease process.

    How to Cope with Dog Cancer

    If you're like most dog lovers, the thought of your dog being diagnosed with cancer is something you simply can't bear.

    Learning that your dog has cancer can be a devastating experience. But after letting the news sink in, the best course of action is to learn as much as you can about the illness and what you can do to fight it. Here are some tips on what to do and how to cope when your dog has cancer.

    Unfortunately, as a pet owner, there's not much you can do to prevent it from happening. Every living thing is susceptible to cancer and even if your dog isn't diagnosed until later in life, it doesn't mean they necessarily lived an unhealthy life.

    The good news is that there are ways to cope with a diagnosis. Here are some things to keep in mind:

    If you want to know how to fight cancer in your dog, you need to learn as much as you can about it. You are probably familiar with some cancer treatments, such as radiation and chemotherapy, but the more you know about each cancer treatment option available, the better decisions you will be able to make for your pet.

    We know how cancer is generally treated with humans, but cancer treatment for dogs is not exactly the same. For example, chemotherapy for dogs is just used to slow the growth of the cancer or reduce the size of a tumour. It is not intended as a cure, as with humans.

    When making decisions about your dog’s cancer treatment, you want to get everyone involved. Talk to your spouse, your family, your vet, a veterinary oncologist, or any other specialist who has been recommended to you.

    Try to have a forthright and wide ranging discussion about all of the options that are accessible before making a decision regarding treatment.

    Often, trying to deny our feelings and our emotions only makes things worse. There is nothing wrong with feeling sad and grieving about your dog having the disease. It sometimes helps to write about your feelings and talk to others about what you are experiencing.

    Keep in mind, you want to maintain good spirits around your pet, they can read your emotions, and if you are acting depressed, it will affect your dog and make them anxious or out of sorts as well. 

    Treatment Options

    There are types of cancer in dogs that are very treatable. After receiving an accurate diagnosis, it’s important to also ask your veterinarian or veterinary oncologist if the cancer has spread. Tumours, for example, can often be removed, but the cancer cells may spread to other parts of the body and that could affect the type of treatment you seek for your dog.

    After getting a diagnosis, your veterinarian may refer you to a veterinary oncologist to determine the next steps. They will talk you through the various options, depending on the type of cancer your dog has.

    According to Dr Diane Brown Chief Executive Officer and Chief Scientific Officer for the AKC Canine Health Foundation in the US “Options may include surgical treatment, combination therapy of surgery and chemotherapy, radiation therapy, chemotherapy alone, and immunotherapy. Immunotherapy includes cancer vaccines — there’s a cancer vaccine for melanoma available for dogs now.”

    Surgery tops the list of the most common strategies. Removal of a malignant tumour with complete margins—encased in healthy tissue—offers a hopeful prognosis. Surgery is also used to improve a dog’s quality of life.

    For example, in the case of leg-based bone cancer (appendicular osteosarcoma), amputation of the affected limb can significantly reduce the dog’s pain. While it isn’t necessarily a cure, it helps a dog be more comfortable. Surgery may be followed by chemotherapy and/or radiation, or they may be used on their own.

    Radiation therapy destroys tumour cells’ DNA and is most often used with solid tumours—carcinomas or sarcomas. The goal is to provide long-term control by shrinking tumours, and, possibly, a cure. Radiation is delivered as either external beam radiation therapy (also known as teletherapy) or stereotactic radiation therapy (SRT).

    SRT is particularly useful for brain and nasal cancers and can require only one to three treatments instead of the 15 to 20 needed for teletherapy. Other types of tumours, such as soft tissue sarcomas of the limbs, can be treated with repeated low doses of radiation, often resulting in a cure.

    Another approach, cryosurgery—or more accurately, cryotherapy, since no cutting is involved—uses liquid nitrogen to freeze small skin and subcutaneous (under the skin) tumours; it reportedly has a very high success rate.

    Swelling, reddening, and occasionally pain and lameness are among the possible side effects. At the upper end of the temperature scale, hyperthermia uses heat to damage cancer cells, and is almost always paired with other forms of therapy rather than used as a standalone. On its own, it has few side effects.

    Many of these approaches have been used for decades, and their limits and therapeutic potential are well known. However, in recent years, more options are being tested in vet school laboratories and clinics across the US.

    Among them, immunotherapy, where you’re basically taking the dog’s own immune cells to kill its own cancer cells. It’s a way of weaponising a dog’s immune system to take action against a cancer by recognising the danger and destroying the cancer cells.

    Another recently developed approach involves sequencing a tumour’s DNA to identify cancer-causing mutations and then using a customized drug therapy to attack the cancer cells; the treatment is delivered in pill form and can be administered at home.

    And then there’s metabolomics, the large-scale study of very small molecules. At the Cornell College of Veterinary Medicine, a study of a type of lymphoma common to both people and dogs began in mid-2020. To look for metabolic changes similar to those found in people with lymphoma, blood from healthy dogs is being analysed and compared to samples from dogs who’ve been diagnosed with this cancer.

    Depending on the type of chemotherapy, the dog might receive a pill, injection, or IV. Many of these appointments are similar to regular veterinary experiences. On the other hand, radiation therapy requires anaesthesia to ensure the accuracy and positioning of the treatment. Dr Brown also stresses the importance of considering pain management, quality of life, post-op care if surgery is involved, and nutritional therapies.

    Chemotherapy may be offered alone or along with other interventions, such as surgery or radiation. Drugs may also be given orally as a pill your dog can swallow. Chemo may be administered via an injection at a veterinary appointment.

    Side Effects of Chemo

    Some common side effects of chemo on humans, like nausea, vomiting, and low energy levels, are well known. Unlike people, dogs rarely experience the side effects common to humans; 70 percent suffer few, if any, side effects because dogs usually receive lower doses of the treatment and often have fewer additional drugs being administered, they may experience milder reactions to taking to chemo. For example, most breeds typically do not lose their hair like people do.

    That being said, dogs may experience some mild, moderate, or severe appetite loss, vomiting, or diarrhoea. Decreased white and red blood cell counts may lead to a greater risk of infection. Lastly, some dogs may experience lethargy due to the treatments. If your dog experiences any clinical signs that seem out of the ordinary, these should be discussed with your pet’s veterinarian.

    Cost of Cancer Treatment

    And then there is the cost. While some pet owners will spend whatever it takes, the truth is not everyone can afford thousands of dollars’ worth of treatment out-of-pocket. The cost of chemotherapy, for example, can range from R45,000 to more than R150,000. So even though this is an emotional time, you will want to consider the issue from all angles.

    In South Africa you can explore options for Pet Insurance to cover the cost of cancer treatment. Many of these policies might have a standard 12 month waiting period from the inception date of your policy. This means that after 12 months starting from the date your policy began, your pet’s cancer treatment will be covered.

    Cancer is considered to be a pre-existing condition. A pre-existing condition means a medical condition that shows clinical signs before your policy began. So in short, cancer will be covered after one year of paying premiums. Which can be a great help as cancer treatment often involves ongoing medical care, so although you have to pay for the expenses for 12 months, after this waiting period you will be covered.

    But, by having pet insurance, your dog will still be covered for vet costs that are unrelated to cancer. These include accident cover, illness cover and routine care. Each pet insurer will have a number of different plans for you to choose from.

    Remember that cheaper is NOT always better. Ensure you read your policy wording document and know EXACTLY what you are and what you are not covered for.

    Like all insurance products, consult a qualified, FAIS accredited broker for advice and more guidance.

    CBD and Holistic Options

    Cancer is a devastating diagnosis. It affects the patient, it affects the family, and it can be incredibly difficult to watch your furry best friend suffer with it. And while there are hundreds of different cancer treatments available today, many of them come with serious side effects and an extremely high price tag. But you know what doesn’t - CBD oil!

    Yes, you read that right. CBD oil may be the key to unlocking a healthy future for your dog with cancer. CBD is a cannabinoid, or chemical compound, found in the cannabis plant. “Cannabis” usually refers to the marijuana plant, but hemp is also a type of cannabis. Hemp is a source of CBD.

    CBD is a non-psychoactive compound, which means it won’t get you high, unlike THC (Tetrahydrocannabinol), another cannabinoid found in the cannabis plant. Humans and animals alike have an endocannabinoid system that receives and translates signals from cannabinoids.

    It’s responsible for bone growth, appetite, pain sensation, mood and memory. The endocannabinoid system plays an important role in regulating a broad range of physiological processes — including pain sensation, mood and memory.

    CBD interacts with this system to produce many beneficial effects on our health. Because of this interaction between CBD and the body’s endocannabinoid system, research shows that CBD has multiple benefits for treating cancer symptoms as well as cancer treatment side effects.

    How does CBD work?

    When your dog gets cancer, it has different effects on vital organs like the heart or liver. Those organs can weaken or fail due to cancerous cells rapidly dividing and growing into tumors that press against their surrounding tissues.

    It’s recommended dog owners keep an open mind and consider an integrative approach, using the best of both the west and east. Many owners still choose alternative therapy for cancer with fewer side effects. So, what is alternate, eastern treatment?

    This could include diet, Chinese herbs, western herbs, essential oils and supplements that all have cancer cell killing abilities. But the main focus is to promote an environment in the body that promotes the health of normal cells but discourages the growth of abnormal cancer cells. There is no generic treatment for all cancers so treatment must be targeted. 


    The bottom line? As our best friends, dogs deserve the most comprehensive cancer care program you can provide. This includes annual physical examinations, vaccinations, and routine testing that helps to identify any potential signs of cancer in their early stages. Of course, you won’t be able to stop every dog from developing cancer, but with the right tools at our disposal, you can provide them with the best chance possible to live longer and healthier lives.

    Adapted from the original article.

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